Right. So about a month ago, I got one of these: www.bubbadummy.com
...and I thought I'd write a review of it. I've been using it for about a month, which I think is about the minimum you need to review something grappling-related.
Full Disclosure, Part One: I train at RGA London. The quality of teachers and teaching (and other students) there are excellent, but if I've got one complaint it's that there isn't a huge amount of drilling there. At the most you'll probably get to do a move ten or fifteen times before you move on, and I'm not the sort of chap who can use a move in his game after doing it ten times. This has been the same at most places I've trained, so that it's almost an accident which moves end up as part of my grappling vocabulary. If I get the opportunity to hit them a couple of times after learning them: I remember them. If I don't, I don't. This was why I bought the dummy.
Full Disclosure, Part Two: I live on the ground floor and have a very tolerant girlfriend.
Construction: this thing is nicely put together. The poseable joints bend into pretty much every position you could put a real partner in, and will mostly stay in the positions you put them in. Cranking on them so far hasn't affected them, and although it seems to be put together from sturdy wires and duct tape, I have no idea how: I could not make one of these things. Its ribs are sturdy enough that you can happily sit on its chest, and its head even has a nose. It's also very heavy: I got it off eBay, and it's the 50kg version. That sounds light, but they only sell it at 30kg now and I can see why. It's already headbutted me once, and that *hurt*.
Training: You can probably imagine basically which moves it's possible to do with a dummy, but here's an extended take. Standing guard passes work really well, as you can basically bend the limbs out to mimic somebody spider-guarding you - although obviously you won't get the same pressure. Moves from mount and side mount are great. Leglocks (I've been working on some stuff from Reilly Bodycomb which are against BJJ rules) work great. Submissions from guard are more tricky, because it's difficult to get the right pressure from the dummy - but I've been practicing some rubber guard stuff with reasonable success. Sweeps from guard are tough, because you can't really get the dummy to posture up on its knees properly without tying its legs together. Guard breaks aren't that useful, although you can simulate a closed guard/halfguard by tying its legs together. Escapes from mount and sidemount aren't the best because you aren't getting proper pressure from your opponent. Moves that require the dummy to be on hands and knees (stuff from sprawl control, say) require you to tie the dummy's legs together. Anything with you on the ground and the dummy standing clearly won't work. A general rule of thumb is, if you need to 'feel' an opponent's pressure or balance to make a move work, you aren't going to be able to drill it properly with the dummy. The website claims that you can practice throws on it, but that seems ridiculous. That still gives you a lot to work on, though.
Results: My grappling has definitely improved. Bearing in mind that I've had it for a month, moves that I've nailed in sparring that I had *never tried on a human* include: the Peruvian Necktie, a collar-choke flow from Roy Dean, a Demian Maia variation of the Matador pass and an X-guard escape that I got from Jiu-Jitsu University. I've learned some other stuff that I just haven't been able to try yet. That's as much empirical proof as I need that it does actually work.
Thoughts: How much use this dummy is going to be to you is down to two things: how convenient it is, and how dedicated you are.
I've got a girlfriend who lets me leave it in the living room for days on end and at worst put it in a cupboard, and as such it's always there - if I had to go train in the garage with it, or wait until I was alone in the house, it wouldn't be as useful. As it is, it's like having a training partner who never demands a go, or says he's tired, or doesn't fancy training. If you want to do a move 100 times you can. If you're reading an instructional at midnight and need someone to try the move on, it's there. If you've got ten minutes before breakfast, you can bang out some reps of that move you're going to try in the evening. I can't emphasise enough how useful this is.
But that wouldn't work without discipline. I enjoy jits, but more than anything I enjoy feeling like I'm getting better at it, and going from class to class without a structured way to improve was getting to me. Training with the dummy is boring, but if you've got the discipline to do those 100 reps, it will get you results. Look at it this way: if you're the sort of guy that ends up chatting to your partner during the drilling bit of class, you might not get much out of it. I'm a big believer in Eddie Bravo's idea that doing a move should be as instinctive as tying your shoes, and if you do enough reps, it will be.
Was it worth the money? I paid £400 for it, and that's four months' jits for me. Whether it improves my game that amount remains to be seen, but I think that if I stick with the drilling it absolutely will. I'm really glad I got it, and that's about as much as you can ask.
I'd be happy to take questions from the floor.