Opsite flexfix is a bit thicker then tegaderm. It does not flex as well for me and tends to lift around the edges and get skankier then tegaderm does.
I used to put it around my Dexcom to keep it on better, but have found that if I use tegaderm under the G4 instead of on top/around the adhesive patch I get a secure placement that will stay securely in place for three weeks with out coming loose. I get a tiny bit of lift on the edge of the tegaderm by the end of my sensor life. The tegaderm is thin enough that you can place the Dex sensor through it, can't do that with the flexfix.

Have not needed to anchor infusion sets, so far, and when I used the opsite to a anchor a loop it was more trouble than it was worth. Had a lot of skin irritation and since I use a slant set it was more restrictive of movement and less comfortable.

With aggressive cleaning protocol before placement I can ran run a site longer. With a manual insertion slant set I can check the insertion site and pull when any hint of an issue. Since I have a low TDD, and my pump has a microdelivey system I maintain good absorption. I do use skin prep wipes after cleaning so that adds a bit of extra sticking for my infusion sites.