To help out, from a "long standing owner"
I've had 4 intercooler setups. 2 of the original ones on the M12 and M400, the "Faulks" upgrade (more internal surface area plus a fan) onthe M12, and now the Pro Alloy one with and without fan on the M400. Swaps have been "as per the instructions" with nothing else done.
Here is my experience :
All of them have suffered from causing the engine to back the power off, so none are "perfect". The worse is the original intercooler, where on hot days it would be backing the power off even if you were travelling at some speed.
Removing the rear number plate is better than leaving it on and changing the intercooler in every case I could work out.
The pro-alloy intercooler seems to sort itself out easier when it's failed to cool things better than any other one. The original intercooler, once too hot, would never cool back down and so you were pretty much stuffed with lower power.
Fans seem to give varying results. They improve some situations (standing traffic), but probably are worse (nothing definitive, but I feel the power drop less overall now I have taken the fan off the pro-alloy one) when you are moving on. I am toying with the idea of building a small shroud and putting two fans on, but that's mainly an idle thought.
Much discussion has been had about the design of the ends of the intercooler. I'm no expert, but as the killer seems to be the heat, not the flow of air, I personally think, compared to the standard intercooler, it's irrelevant.
So, is it worth it? Probably not, but neither is almost anything else you spend on cars, and it does make an appreciable difference to when you get that "strangled" feeling from the engine when the ECU has backed the power off. You get that far less with the Pro Alloy intercooler, but it still happens so isn't the "perfect" cure.
From what people post on here, the perfect cure requires lots of reflective tape, wrapping the entire exhaust system, turbo jackets, new seals for the intercooler box to the clam, and moving the rear number plate. All are far too much faff for me