1) I presume that 50 ppm is the concentration of available chlorine from the tablet. This is a very low concentration to cause corrosion in 316. The corrosion will be evident in 304 faster than 316, that too after a long time. It depends a lot on your cleaning frequency also.
2) Except for difference in handling of hypochlorite and tablets, I don't see a major difference. Both of them will form Hypochlorous acid on dissolving in water.
Hope this helps.
IMEX conc. solutions of sodium hypochorite (eg 10%) as typically available are very unpleasant to handle in bulk (eg 20L). And somewhat unstable. But they are also cheap.
Calcium hypochlorite powder is also extremely nasty in confined spaces and potentially "explosive". Hi-Grade Pellets are a bit better but expensive.
Crytalline formulations of other hypohalites also exist which are nice to handle (~odourless) but are very expensive.
But it's possible some other commercial hypohalite product exists which i haven't seen.
The isocyanurate sounds nice but i anticipate is not cheap. This old thread discusses its usage in the "field" -