That's because it is an MT4 and an MT5? The only difference is the HC blade and "TRAIL" written on it rather than "FIVE".
Aside from when Mantel are chopping stuff out cheap the Trail setup is the one I'd go for just because it's pretty cheap for two very good brakes.
Semi-related, the HC blade fits all their brakes from the MT4 up to the MT8 (officially, at least - I've got the HC blade fitted to my MT2 lever body with no problems), so there's not really any performance advantages inherent in the lever itself apart from the BAT adjuster. That said, the BAT adjuster seemed to be the source of all my problems with my MT7s, and seem to lead to most problems our customers mention, so the MT5 is probably a better bet in that sense.
I just found this deal on mantel.com I've got mine for the same price not so long ago. Shipping is very quick and the price is awesome.
It's only this weekend though so you need to hurry up.
Magura MT5 Next for £59.00
Yeah the better the rider, the less demanding he is when it comes to brakes.
The MT Trail Sport looks more like an MT5/4 than a 7/6. That's the standard, not uprated lever.
Therefore I'd give it a miss. MT5 or above.