So after waiting to hear from Airsoft GI on my pre-order and then finding out that it would be late September I was able to cancel it and grab one from Toronto Airsoft.
I used it at Ultimate Airsoft on the weekend and overall it's a handy piece of kit.
I use G&P midcaps
http://www.evike.com/products/42513/, and compatibly was fine. There is no magazine catch or release, it's just a press till it clicks deal.
With the loader fully loaded (claims it holds 1800 BBs) it was super easy to load the bottom raceway that you pump to load the BBs, you hold the loader straight up and just tilt down a bit and the BBs flow out great. I estimate that once you get to around the half way point of the reservoir it becomes a little tricky to complete fill the raceway with 40 BBs, you have to play with the loader to find the sweet spot. It gets more frustrating as the reservoir gets lower so I recommend just topping it off once the loading becomes cumbersome.
The action is very smooth, you basically pump like a shotgun and if the magazine is full the handle stops or it skips a bit which doesn't sound nice but reading the manual and checking online I haven't seen any indication that it damages the loader.
I was able to fill my 9 midcaps very quickly with the full loader. Just for shits and giggles I will time it sometime this week to actually have a number via the traditional speedloader and the SL14. I estimate it's probably 3 times faster but I'll try and get some numbers to back that up.
In terms of carrying this out in the field it's big. I have a Condor Convoy Pack
http://www.condoroutdoor.com/Condor-169.aspx and this thing still sticks out of the main compartment with the zippers closed. Also it's loud, the BBs rattle around too much for my liking. I would look to line the reservoir with something to absorb the sound if I really wanted to lug it around.
At around the cost of 6 regular speed loaders it isn't cheap but build quality seems good. I believe if you run a lot of midcaps this unit would pay off in the longer events where you'd like to minimize your downtime. Also if you have a team of players this unit could pump out around 14 midcaps (120 rounds) before you fill it again but as I mentioned at the top I would fill it up more often to keep the speed of the system up.
Oh, in the future it should fill other magazines. The adapter is easily removable but only time will tell how Elite Force supports it.
Any questions fire away, I'll update this post with the actual speed sometime this week.