That's just high-priced sight paint. You can get Testor model paint a lot cheaper and it works just as well if not better. A couple of tips -- lay down a coat of white paint on your sight first and then when it dries lay down the colored paint (orange or yellow or whatever you like). When that dries, put on a coat of clear fingernail polish as a sealer. Works great!
I tried some of the Brightsight paint on a tiny KelTec P3AT (380 auto-loader) when my 60 year old eyes could not resolve the sights. I outlined the groove in the rear and painted the ramp of the front sight. The yellow-green color permits me to pick up the sights much more quickly.
As others have said, model paint likely would work just as well.
I guess I'll be the lone dissenter to say I've used both model paint and the bright site stuff and I realy like the bright site paint. I used white to fill in the dots on a CZ clone. Still very bright white and hasn't been affected by solvents 3 or 4 years later with lots of rounds through it.
It's spendy for the amount you get but it's still only 6 or 7 bucks. That's not too bad if you decide you don't like it.