I have one, and its very good overall. Give the cost of a setup, the issue with the standard batteries are a major drawback but if you get this fixed from the start you are on to a winner.
For range and reliability the TM next gen M4s are top notch. I lent mine to a mate. Normally he gets 5 kills in a day. He was raking up 15+ a game and couldn't keep a total count from the day.
Pros
All metal, good weight
small kick you get is very addictive, you wont want ot go back to a regular AEG. It really makes firing and kills more rewarding. Try one and you'll understand.
The realistic firing, stop and bolt release, when using mid caps is actually good fun to use. I sometimes alternate play from mid to high caps as the mags feed very well, so semi-auto can be totally relied upon.
RANGE BABY - you will be the envy of everyone (without one of these or a systema). They go for miles (slight exaggeration possibly!)
The CQB-R and the sopmod both have great range, you will not see a difference between them with the hop set right, so just go for the look you like. They also do an AK and a SCAR is coming out.
Cons
Low fps - mine was 290 out the box - can be upgraded to 350fps- special springs are a tenner. This increases range even more and makes your enemies hit taking more of a certainty.
Stock pipe nut and barrel nut need tightening regularly with all the shaking. Get a gunsmiths tool and keep them tight.
BATTERIES. Expect to spend some money sorting this out. The standard 'quick change' 8.4 NiMh are worthless, do not buy any. Make sure you get a lipo conversion from the shop you get it from. 7.4 lipo shoved down the tubes that the quick change fit is can last a day. sorted.
ROF - you will get a reasonable ROF but if you want minigun style 20 rps+ you will not get it on this recoil platform.
Mags, you will need the special mid caps to keep the bolt release feature working. You can by an adaptor though to allow you to use any standard M4 mags.
Good luck