Hi everyone - I've just spent some time with the mod & just had to quickly chime in
It's surprising good actually - I didn't expect it to be as good as it is. The choice of modes is excellent and really varied. On the one end of the spectrum, you have the de-blur option - the image is line doubled and rendered in super sharp pixels. Some people seem to like this, but it's definitely not for me. The image is very pixellated - graphics in the distance degenerate into indecipherable clumps of pixels. In fact I avoid all the sharp pixel and direct modes as I've always disliked line doubling with the N64. It's all a matter of personal taste of course, but to me this isn't how Nintendo intended their games to be experienced. I think they wanted their hardware anti-aliasing to counter heavy pixellation and when it wasn't overdone and used well it could look amazing on the right display.
At the other end, you have the retro mode, with dynamic scan lines, bloom etc. This is better, but a touch soft to my liking - I adjust from the individual settings instead (no overscan, HV bloom etc). I keep Hybrid scanlines though - in brighter areas, the scanlines bloom and blend like a real CRT although the effect is a little overdone, as if the CRT had the contrast set too high. It'd be nice to have a setting to reduce the effect a little - but the overall effect is nonetheless really nice as long as I'm sitting far enough from the TV (about 10-12 feet from a 46" screen). Any closer and the flaws in the image start becoming more apparent.
Similar to the Framemeister scanlines, there's the option of 'simple scanlines' with varying intensity settings (but no blooming) - but I preferred hybrid. The hybrid mode combined with gamma boost gives a very CRT-like image. For me, It's not quite as nice as a good CRT with RGB though - but close - much closer than I thought it would be. To me, the CRT + RGB connection just handles the image a touch better . A little more forgiving, smoother, less pixellated, but still very clean and without any lost detail - combined with that lovely, unique punchy glow of real CRT phosphors. I think the effect is a slightly more pleasing and cohesive image, although I expect the difference won't be much (or any) of an issue to a lot of people. This will be improved upon in the future when we finally get true hardware dynamic phosphor emulation in 4K OLED. It's also worth mentioning that I'm using a plasma which tends to be a little more forgiving than LCD for SD material. I don't think it would be a factor but I don't have an LCD to test it on.
All in all, the mod definitely looks quite a lot better on my HDTV than a direct RGB connection. The cost is high but I think it's really worth it for dedicated N64 players who don't want a CRT. The 16ms lag didn't bother me, but then again, my TV has low lag. Hope this is useful!