I haven’t tried the optics from Convoy, but I know Yajiamei Optics are great and the go-to single LED optic on BLF. I have many of them in modded lights.
The thermal protection does help a bit, but when the light is below the temperature threshold the LED will get full current on high mode, if the battery voltage/type of battery can supply enough power.
I don’t have an S2+ anymore, so I’m not sure if that optic will fit. I know the Yajiamei Optics fit without any modifications. And I can confirm a Luxeon V does not fit under a 3535 optic, it’s 4040. You can use a reaming tool to open the optic a bit but then you need to raise the optic a bit with a shim to make up for the lost height when reaming it, otherwise it’s out of focus. I just reverted back to a reflector for my Luxeon V.
The best results I had WITH 20mm Yajiamei beaded optics were SST-20, XP-L HI, XP-L HD, LH351D (in that order throw to flood). And I have only tested 10, 15, 20 degree 20mm Yajiamei beaded optics.