Ditto on the Luigi. I have two with grips that are just little bumps, not very pronounced, and yet are very adequate. And I have an older Luigi with a barely noticeable bump, even smaller than the others. This is the one I keep on the M2. And this, too, is very adequate for all but a heavy lens. I don't think I'd like a case with the very pronounced ones I've seen pictures of. The Luigi case feels luxurious, and as Gerry M said, feels very good to hold.
I have the Leica M Grip, but after the novelty wore off, I rarely use them. If I get another 90 Summicron, then I'll use it. Maybe. The Luigi case is a nicer way to hold Leica.
The Tom Abrahamsson grip is very substantial and should be great for heavier lenses, but it might be overkill for a 50mm f/2. I haven't tried it.