I just got the Well R4 copy of the TM MP7 from Airsoftworld as they have it for £70 at the moment. It is a direct Chinese copy of the TM with all parts interchangeable.
https://www.airsoftworld.net/well-mp7-aep-airsoft-smg.html
I bought it as I was curious about it as a PDW, and thought it might be a fun and handy back up gun.
It's a good fun gun, and whilst not the TM, I imagine that it is broadly similar performance wise if a bit less on the quality side. Its really not bad at all for what it is, a cheap Chinese copy.
I am still using the stock NiMh batteries which to be fare are ok really for what this is, its never going to have stunning performance, but yes a LiPo will improve the trigger response, but do also remember that used straight with no mosfet a LiPo may also burn the trigger contacts quicker, which I would imagine are quite small in this beastie too. Remember too that this does not have an airsoft motor with replaceable brushes, it has an RC can type motor which does not have changeable brushes, and again using a LiPo may cause these to wear or burn more quickly, and thats then a new motor needed.
As for fitting a mosfet I am not sure where you might fit even a micro one as space is really tight given the size of the gun.
Honestly I would not waste much money on upgrades for one of these, even the TM version, it is never going to have "great" performance no matter what you do to it. The performance on the AEP type MP7s is always going to be limited by the size of the internals. There is only so much you can squeeze out of something this small lol. You can fit a stronger spring, but you just can't get a bigger cylinder or other performance improvements in there so most mods will really be limited to efficiency improvements and small in their performance gains especially on the TM where the hop bucking, air seals etc.. is already pretty good.
If you want an MP7 with superior performance then I think the GBB ones are the only way to go.
As to feeling hits, its accuracy is not great so actually in some situations being able to tell if you have hit someone or not at range with a single shot is going to be harder and likely to cause as many "I hit you? No you didn't!" problems as the target not feeling it I would have thought. You may not feel the odd hit, but you are most likely to want to have this thing on auto to get its full effectiveness and missing a hit from a string of bb's would be much less likely.
In conclusion I would say it is an up close and personal defence weapon and as such a great back up gun to pull out and spray a good amount of BBs at a closer ranges. As a primary even in CQB it would be lacking in too many areas to really work well in my opinion, and the GBBs would probably be a better option for an MP7 style primary weapon in that and most other scenarios.
Think of it as similar to an Automatic Electric Pistol, because that is what it really is, just wrapped up in an SMG outer shell.