I had a Radiance when the HD621 first came out-I think I got the HD621 as soon as it was avaialable. There were problems at that point and the Lumagen people did some work and realized not that M's implementation of HDMI was crappy but that it was actually observing the HDMI specs more rigorously than nomal-something about an extra bit in the transmission or something like that. Once they figured that out (after some discussion with M) they put out a revised software and since then I've never had any sort of problem.

The problems you mention were the sort I remember encountering way back when the HD621 came out but I'm surprised that they couldn't be resolved.

Anyway, I would not do any serious movie or TV watching without a Radiance in which the display is calibrated using Radiance's CMS. If, however, you are happy without it, good for you. Save some money for some other toy!

MD600(2x2TB); iPad Pro
LR. 818v3, 8000SE
HT. 861v8+ID41,HD621; BW 2x802D,HTM1D,4x804S;SVS sub; Mac 5 MC501s; RGP 600Pro, JVC X950; Radiance Pro; Oppo 203
FR. G65, DSP3200-3300 DSW, HD621; Mac MC152; Oppo 103, PDP TCP65VT60, Radiance 2124; RGP1200C
4. G65, DSP3200-3300,HD621; OPPO 83, Radiance XE PDP
5. 818v3; Prime HP Amp; HD800