I get your point.It appears to be 25% more in weight compared to the original battery (~339 grams). So that's only 83 grams. Well within the payload capacity. If it ads 10 extra minutes to the maximum flight time that's about 20% and add a bit more for the plastic and stuff. I mean if you want to fly for an hour with enhanced transmission that's an option. Perhaps you would've come back with plenty of battery left and no stress as long as you thoroughly tested it first.
But, let's be realistic.
Real world, you'll get 50mins from that type of battery. Similar to the standard M4P battery, 40mims in the real world, instead of the quoted 51mins.
Is the extra 10mins worth the extra £100 - £150? Not really, when I can get another brand new genuine M4P battery for that money.