Thank you Sue! I appreciate your research and answers.

I use an algae based calcium supplement, New Chapter Bone Strength. A daily serving of 3 pills has 905mg calcium, vitamins D3, K1, K2, magnesium and a trace of Stronium which occurs naturally in the algae. A 40 day supply on Amazon is $40. I've used it since I was diagnosed with osteoporosis 6 years ago and my DEXA scores have remained stable. I am due for another DEXA in a couple weeks.

https://goevomed.libsyn.com/contrversies-in-nutrition-nac-strontium-and-fish-oil
This podcast says it all about the efficacy and safety of strontium citrate.

Thank you for researching!
AlgaeCal’s Strontium contains Strontium citrate, not the controversial version - Strontium ranelate. Hopefully that clarifies why some are seeing safe results with it?

But these studies are about strontium ranelate not strontium citrate in Algaecal

Here is a posting of research and studies on strontium research which might be helpful to you in your deep dive into strontium research. Notice the bone biopsies and the 2020 review of strontium research etc.. https://www.inspire.com/groups/bone-health-and-osteoporosis/discussion/dd823b-strontium-a-compilation-of-research-and-information/
Also, notice the TBS research and newer Rems information.

In the research which you cited, but did not discuss, about the interaction amongst calcium, strontium, and citrate ions, notice that the addition of strontium was found to increase calcium bioaccessibility from calcium citrate suspensions at different temperatures. ( a partial quote from the research)
https://www.sciencedirect.com/science/article/pii/S0167732224000151#s00600
I see that you may have misread part of the 2021 research when you say that oral Strontium Ranelate does not affect bone formation. Notice that your provided quote is referring to bone defects not osteoporosis and is in the section discussing local use of strontium for bone defects not osteoporosis. This is not a quote about osteoporosis but about the need for strontium laced materials to be applied directly to the site of the bone defect.
Titled "Local Administration of Strontium Ions". The quoted portion which you provide contrasts the use of strontium used directly at the site of the defect as opposed to oral administration and then points out that strontium is needed directly at the site of the defect rather than orally. It is not negating the use of oral strontium for conditions such as osteoporosis. see acutal osteoporosis quotes from the article below
To reiterate
You say:
"Later in the article they add: "Orally administered strontium ranelate does not significantly affect bone formation in vivo because it does not reach a sufficient concentration near this tissue, assuming a standard drug supply and a normal calcium-rich diet.""
This is a statement about specific bone defects not osteoporosis. No one doubts that specific areas of bone damage need a more concentrated application of strontium. Multiple research upholds this as does current use.
Strontium laced products applied directly to the area of concern are being used in multiple ways for bone defects, jaw necrosis, cranial burr holes. see my first linking of a compilation of strontium research where there is a list of such applications
When osteoporosis is discussed in your 2021 linked research, rather than bone defects, the article says: "Strontium can also be incorporated into bone cells, which increases their density and reduces the risk of developing osteopenia and osteoporosis. "
Then this statement about osteoporosis, strontium and fractures is found:
"The SOTI (Spinal Osteoporosis Therapeutic Intervention) study found a reduction in the incidence of spine fractures in postmenopausal women after just one year of treatment. This decrease, compared to the placebo control group, amounted to 49%. A three-year double-blind study showed a 41% reduction in the incidence of new spine fractures, compared with a placebo group. TROPOS (treatment of peripheral osteoporosis) studies have shown the effective anti-fracture effect of ranelate on non-vertebral fractures within the first three years of use. These fractures were reduced by 16% [37,38,39]."
Plus, a long discussion of how strontium works with osteoblasts and osteoclasts to form bone.

Strontium citrate is easily obtained as a supplement in itself without the price tag of the AlgaeCal products. AOR and Vitacost are just two providers.

Part of a deep dive into strontium might be to research the newer bone tests such as REMS and Dexa with TBS. Both of these bone scans show that strontium users have good bone density and good bone quality. The research of Dexa with TBS shows that strontium users place within the top three of bone quality results. Page 7 of the research, https://www.panoramaortho.com/wp-content/uploads/2019/03/TBS-Review-JBMR-2014.pdf
see further research in the first provided posting of strontium research at the top

The discussion of strontium ranelate, its differences and its complicated history in the European medical community makes for a long and involved posting. It may be found in my first linked offering above.
Probably the quickest answer is that strontium ranelate is not available in the USA. Strontium citrate is available and strontium citrate has never been banned or limited in its use. I do think that further testing would be helpful, but the current testing and research has not found strontium citrate to be associated with any cardio vascular problems.

There is a tendency to "poo-Poo" strontium use in terms of osteoporosis results. This probably has to do with a back lash against the Naural vs Medical discussion. My use of strontium for my once osteoporosis now "normal" bones is based entirely on research and on my doctor's recommendations. There are not many osteoporosis treatments which have years of research, bone biopsies, plus good results from DEXA, REMS, and TBS and an almost non existent chance of side effects. Strontium is hard to believe, but a read of the actual research and studies at least says that this is a supplement which needs more study.
Thank you for the discussion.