TM will be awesome guns and run forever - as long as you're happy with 280 fps and don't mess with them. If you want true performance you basically have to gut the gun and replace most of the internals. Try upgrading a stock TM V2 mechbox to 400 fps without swapping anything but the spring and you'll be picking bits of metal and plastic out of your broken shell in no time.
IMO, buying TM M4 is a waste of money, because you have to sink a bunch of money into it to make it a good performer. You can get a clone and put the same amount of work into it and have it come in cheaper than the stock TM, and in the end, you'll have a much better gun.