I use a mild PT weekly (Aphogee 2 minute reconstructor), and I find that it seems to keep my hair strong and pliable. 3 months ago, I started using MT as a growth aid- I "grease" my scalp with it every other day. It definitely affects my moisture retention though and I need to stay on top of using a heavier moisturizer and sealer since I've added it to my reggie. It has taught me that I'm sure my strands could not tolerate using a heavy PT on their length on a regular basis.
I use Aphogee 2 step every 6 weeks on my oldest daughter's hair- her strands are EXTREMELY fine (although very dense) and her hair breaks easily. Since adding this, and other protein to her reggie, she's progressed nicely from APL to BSL since September.
HTH