I have two weighted vests, one that goes to 20 pounds (XVest2) and recently bought a second that goes to 40 (original XVest). They are the type that lets you adjust by adding/removing one pound lead weights, and they are in the "expensive but worth it" category
I've been using them in Meso1, mainly for leg exercises such as squats, step up/leg presses, lunges (not deadlifts). 20 pounds recently, and I'm expecting to go higher for Meso 2 and beyond. Also, sometimes I use up to 10% of my body weight in a vest for cardio and hiking.
I like the vest for STS Legs because ...
* I didn't have to start out with a full suite of dumbbells and also was able to put off buying a barbell for a month, while still meeting my weights. A pair of 30s plus the 20 pound vest got me through the first few weeks of squats and leg presses.
* It significantly cut down on forearm pain while letting me gradually build strength. I can shift weight from my core/vest to my my hands/dumbbells as I get stronger, without compromising my legwork. I'll use the vest even if I have other options when I feel my arms getting tired.
* Personally - I feel that having more weight balanced evenly on my body and less in my hands is helping reduce shoulder, knee and elbow pain during dynamic lunges. Probably it's a form issue - but I find that even when I focus on using muscles to stop the swinging of a weight, I still feel it in my elbow. And, if I don't slow down the motion fast enough, it seems to pull at my shoulders and knees. This doesn't happen so much with the vest/dumbbell combination. I have a much easier time stopping the swing of a pair of 30s (plus 20 pounds in the vest) than if I use a pair of 40s.
* I like the way that wearing the vest in the rest transitions between sets ever so slightly kicks up my HR, probably 10-15 beats a minute. It's small but noticeable.
If I had it to do again I would probably buy just the 40 pounder. When I started STS, I had no idea how much stronger I'd get
But I do like the XVest2 shape a bit more than the original XVest, so since I have it, I use it.
Hope that helps!