I'm also on TRT, and have been switching between LGD and Osta every 10-12 weeks continuously about a year now. It works extremely well for me. I also throw in GW and S-4 when ever it's possible (with 4-6 week breaks). This takes normal TRT to a whole new level, and with SARMs I've been able to cut down AAS use significantly (taken a step back, so to speak), and still progressing, which is great thing to keep health in check.
So IMO/IME it's great to use SARMs to enhance TRT.
S-4 sides depend completely on person and quality of the S-4 you are using, so I wouldn't rule out using it before you try it yourself. For example I'm able to get up to 100 mgs /day before experiencing any noticeable vision sides, and still at this level they don't bother me in anyway.