Yes, they are a lot better than the stock set-ups. There are two basic ones, the R-Hop and the ER-Hop. The R-Hop is just the size of the stock barrel window, but the ER-Hop is longer and needs the window modified. The patches with the letter "I" in front of them just mean that they're more efficient in colder weather if I'm not mistaken.
If I'm wrong about anything, somebody please correct me. I'm not sure what an M-Hop is though.
The "I" in front of the name stands for "ice" which means it will work in any temperature you will play a game in, while the regular r-hop or er-hop's performance will vary slightly when it gets colder because the rubber hardens a little as it gets colder.
I have never heard of an m-hop but the m-nub is basically a soft-ish nub that is as long as the hop patch is to apply even pressure throughout the patch. You can get it at the same place. You will have to take off the stock nub on your hopup arm to do this though, because it only applies pressure in a single point. I thought r-hop was based off of the g-hop?
Go to the link I posted to read about what the differences are between r and er-hops.
I just used some nerf dart foam when I installed my ir-hop. Cut it to the width of your hopup arm and the length of the patch itself. Glue it on using whatever you want pretty much because it's not going to move around. I used some super glue because I was too lazy to wait for a better glue to dry. The nerf dart foam was suggested to me by cheese and it's been working just as well as the m-nub. The only hard part is getting it centered over the patch. I'm sure you can find a way to work it out.
The modified nub is probably not completely necessary but it is much better than using the stock nub for the previously described reason.
I will probably eventually send it in to Cheese to get an er-hop patch fitted because I use .3g bbs. But the r-hop is an improvement over the normal hopup. especially for lower grade bbs because it stabilizes them better.
I made my VSR hop up arm flat by sticking a cut piece of plastic tubing from a biro pen between the fangs! Much more consistent!
If you don't want to go to the trouble of getting your barrel cut, then get an R-hop. They really will make a huge difference, and don't feel like the R-hop isn't worth it because the ER hop is better!