I have had excellent results from Trimix and have used it dozens of times. I started out with one fifth of a cc (0.20 on a 1 cc insulin syringe with a 30g 1/2 inch needle. Felt just a little prick when it went in (sorry about that!). I have used as much as 0.35. but 0.20 seems to be the sweet spot for me. Very firm erection like when I was a teenager. Stays erect for 2-3 hours. Yikes!! Wife hides.
I haven't had any decrease in sensation. I don't inject close to the head; more along the mid shaft and alternate sides and location. Avoid 6 and 12 o'clock, of course.
It seems if your erection isn't hard enough you might need to gradually increase the dose. I take 5mg generic Cialis every morning. I asked my urologist if it's ok to use Trimix and he said yes, but this is something I would discuss with your urologist. I have read that mixing larger doses of oral meds can result in prolonged (>4 hours) erections-priapism and require medical intervention.
I have found Trimix to be the best solution to my post op/Lupron ED. Although now that I am on TRT I am getting nightly erections again so there is hope.