I do have an SCS and have had the same 2 surgeries as you. My fusion did resolve my spine slipping, so that's good, but did nothing for my damaged nerve root pain (as the Neurosurgeon told me it probably wouldn't, and he was right!).
My background: I still have the damaged nerve root pain from Lumbar to toes. HOWEVER, the SCS handles my back pain very well - just not the pain down my leg, nor the numbness nor the burning and of course, it cannot affect the weakness - just interrupts pain signals. Nothing really showed up on the last MRI I had, several years ago (Radiologist refuses to do MRI's to eval my brain tumor because I have 2 implants now, so haven't had a brain tumor update in 6 yrs, but it's OK anyway - and I did buy the MRI-Approved version!).
I tried 2 different SCS brands during my trial - and only 1 gave any relief down the back of my leg at all.
Both handled Lumbar constant achiness/pain. I tried Medtronic and Boston - and for me, the Boston was better. However, do be prepared for many weeks of adjustments by Techs before you achieve the best results. Due to programming background, they gave me code to do my own programming, and i was able to adjust it nightly until I got it to be the best it could be. I still do rely upon my SCS and use it 24x7. I also still require Meds for the burning feet and legs (it's like standing in a bon fire - all the time! Not even one breath without severe burning, achiness, and pain...in many years). But now I can walk without assistance! I do carry on a reduced, but mostly normal life. Stenosis is also an issue for me. And I can say, for me, it was worth the time, cost and small discomfort of the surgery. Definitely, even though it doesn't cover everything it was designed to cover and they told me it would cover.

I'll be more than happy to honestly answer any questions you may have. BUT I strongly recommend ONLY go with a Surgeon who's had many, many successful SCS's - as I belong to a few groups and have seen some terrible ones!
I would consider asking a Dr to review MRI results as to the screws, etc. That you do have constant pain that may be caused by them, and you want to know if that's correct - or if it's something else. Also, how lose are the screws? That may matter in the future!
Good luck.