Some intersting points raised, copy v branded. With branded I assume that they are build to some form of standard like ISOxxx, BSxxx or whatever it may be. I've never actually checked that out but we all happily buy branded as we think it gives a degree of confidence.
On the flip side though, what are we really worried about with a snorkel? Is it going to let water into the airbox, will it break if I hit a tree and does it fit the profile of the truck
HDPE is much stronger than fibreglass so buy one made of HDPE and ultimately try not to hit a tree. Hit a tree hard enough and HDPE is going to break too.
The UV rating of HDPE, does it really make a difference with the UK sun?
Buy the right one for your truck and it will fit.
Will it leak? As far a I'm concerned this is partly down to taking time over connecting the the flexible coupling to the snorkel body and the airbox. I see no difference in the bottom end of the snorkel body in branded or a copy. It's a round or roundish piece of plastic tube. In fact the snorkel body is not the bit that going to leak at all so branded v copy at this point is a bit of a misnomer really it's the coupling that matters.
Whether you use jubilee clips, with or without a squirt of sealant for good measure the bit that really matters is the flexible tube that comes with the snorkel, is this piece built to a known standard? not sure on that one but the safari report does make an interesting point about 130 degrees rating of the coupling over a cheap example they choose to show.
Lets face it, a lot of off road vehicles have DIY snorkels made from drain pipes and all sorts of bits and bobs, they might not have the right diameter for correct airflow but branded v copy are the same internal profile pretty much.
I see no real compelling argument in branded v copy as long as it's in HDPE ,has been installed with care and diligence and the coupling is adequate rated (or insulated).
Just my view.