I bought an AGM MP44 a month ago or so. I have fired about 8,000 bbs through it without any jams or breakage.
The hop-up out of the box did absolutely nothing even when turned up all the way. I have modified mine slightly and it is better. I have recently modded it a little more but have not retested it.
I found it was shooting accurately: when testing I took a running start, turned, aimed and fired from 150ft, shooting at a 1.5" x 1.5" cardboard box target, and hit target every time (with 1-2 sec. full auto burst). It should be noted the adjustable sights are hard to use with a full paintball mask.
With 0.2g BB's it shoots 430fps consistently. I haven't checked with any other weight yet.
I had to modify a couple of batteries and the wooden stock to get a 9.6V battery for it.
(I don't know if this was a complete waste of time or not, but time will tell)
Note: If you plan on deepening the battery well in the wooden stock: remove trim screws first!
Forever_kaos: what hop-up did you use? Is there a metal, or just even a better unit that will fit? And dos anyone know if a Kar98 sling will work properly on the MP44?