Gary,
I have a Jpoint that was on my 4.75" 83 in 454. Probably put several hundred full house loads and many more than that 250/1100fps plinking loads. No issues with the Jpoint failing. The other hard kicker that this Jpoint has been on is my 458 Socom AR15. No problems there either.
FA makes a mount that replaces the rear iron sight, and they even have a leather holster cut out for it. Pretty easy to modify a nylon holster, or perhaps a leather one if you do not have too much cash in the holster.
The dot sure is easy to use, and the only reason I do not have it on full time is that I wear the gun up at the ranch all the time, and between rain, snow, wood chips (cutting trees), and general knocking about, on the hip, the sight is likley to collect debris. And as the dot is projected onto the glass (plastic), it wouldn't take too much debris to block the sight. It does have a cover, but too much knocking about, jeep seats, door jambs etc. I am always stressing over the cover getting knocked off. Two big thumbs up for the sight as a sight, but I would say you have to temper based on how you will use and carry the gun.
Craig