I've also had an interest in obtaining a Milkor M32 after browsing some reviews on onesixthwarriors.com about the ZACCA P.A.P. chase model in their 1:6 grenade launcher set. I never managed to get one. Well, I finally got a Milkor MGL after a bit of shopping around for a cheap deal.
I picked up the MGL-140 in black over all the other variants. My reasons were simple. But in general, it seems to be the least desirable model based on overall pricing and demand. As of writing this, it looks like the shorter versions are higher in demand. My reason was "get the biggest one in black". I don't care for desert color schemes either. I paid $15 shipped for mine, purchased through a moderately reputable black market dealer holed up in the South Asian seas. They MSRP for $12, so don't expect to get one for under that unless you get lucky. You'll be looking at $17 after the usual price gouging.
Features and Flaws
I don't think anyone expected this review to be all sparkles and sunshine. The Vortex brings out the suck in everything. And my MGL has a good quantity of suck. Let's see what magnitude of suck you can expect.
The slider part of the stock slides quite freely. There's not much of an end stop for the slider, so expect it to completely come off as you adjust it. Due to the way the parts are molded, it's not practical to rig a solid end stop like HotToys did for their M-4's for the Modern Firearms Collection. I can feel a little bump inside the stock where the stop mechanism is, but you can overpower it with little resistance. I'll try thickening the material inside the stock to make the fit tighter so it doesn't slide too easily.
The scope is great. Great if you never want to move it to an angle other than horizontal. There's basic detail on the scope; no fake amber lenses or see-through light pipe. Just a solid block, but that's fine. The optic is loose, and there's no ideal way of making it hold mid position without making some frictional modification to the hinge. The scope base is molded from two pieces with a shared mounting pin, resulting in a pin that isn't snug due to an undersize. The scope fell off enough times during photos that I've thickened the pin with some super glue so it stays on better. Suggest checking your scope mount and making this the first priority modification.
One of the details I liked was the elevation numbers printed onto the side of the sight. From a distance, you'd think it's just a bunch of white lines. It's tough to get a good photo with a crappy camera, but you can see it. The numbers are a bit crisper than my photo shows it to be.
The Chamber and Grenades
The revolver chamber comes marked with the current grenade position on all six chambers in crisp detail. Mine seems to be molded not quite perfectly cylindrical. It has binding spots in certain areas when spun. The cylinder isn't loose enough to do Russian Roulette. As a plus, it stays in place where you want it for photos. If you push the chamber into the front frame, it fits snug so you can hold the MGL by the chamber and not have the rest of it slide away. I don't recommend modifying the chamber to spin freely because of this benefit.
While on the subject of the revolver chamber, I should cover the grenades. They're metal with a fairly thick coat of paint. Part of the grenade tends to hang on a lip in each chamber, so they don't all immediately slide out when you tilt it downwards. Great if you don't like fishing out 1:6 scale grenades in the grass in your backyard. The firing cap is painted on and not molded, so if you do wear that part down for some reason, be prepared to repaint that. Over time, the grenade rims will chip paint.
The frame is a two piece construction, held together by a swivel pin joint. This is perhaps where most of these models will break over time. It's a mere 0.06" diameter plastic pin holding it together. Normally, this would be fine, but from handling the model and opening it a few times, I noticed that it's a fairly stressed component. When you open the grenade launcher to swivel it out, the revolver chamber has a pin that normally locks into a little detente in the rear frame. You need to either slide the rear frame back until the revolver chamber pin disengages, or bend the frame outwards like most people will do. Bending the pin repeatedly will eventually stress the plastic and cause it to snap. A suggested modification would be to drill out a hole in the pin, and reinforce it with a metal rod (or in my case, a paper clip). This will provide stiffness and keep it from snapping off prematurely.
You may be asking "Should I buy one?"
You have no choice if you want an MGL, honestly. You have the illusion of choice between the six variants ZYToys has to offer. That's about it. You're not going to find the ZACCA M32 for a price under $30. You either want one or you don't. Now, if someone would build an RG-6 in 1:6 scale...
My suggestion is to buy the one you like the most, hope QC wasn't asleep/busy whipping the slave labor, and be mindful of the weak points. I don't see any reason to buy the whole set. You don't need all six MGL variants unless you're a ham fisted giant who breaks things by merely touching them.