I've used both companies, and I think they are both equally as good.
Andy at HQ is a mate, and often helps me out if I need something, but then they are only 25 mins from me. Oli is a really nice guy and their setup is extremely professional. Bognor did all my B14 and ARB install and I opted for Bognor for several reasons. Main one being at the time, HQ didn't have the installation setup they have now, and they tended to pass the installation work to someone I didn't personally know. They now have a much bigger workshop, with a dedicated suspension genius. The only downside is they are busy, and as some members know, they are sometimes a longer lead time for installs, which is not a negative by any means. The other reason I drove the 300 mile round trip to Bognor was because they let me use the 300hp TSI monster for the day, and I would of driven that far just to experience a 300hp T6 anyway.
I'm not sure how the £350 gap happened, because most companies up and down the UK that are selling, and installing B14's tend to be pretty much the same price, give or take a few pounds. Are you sure that's like for like comparison? I'd be surprised if
@BognorMotors are quoting too much, equally, if HQ are quoting too little. Something doesn't seem right there.
Lastly, factor in around £70 for a full Hunter alignment, take it from me, it's worth it.
Both will do a sufficient setup, and both will offer a free height adjustment in the future, but if you end up going maximum low, this really needs to have a Hunter alignment, as i've found out to my cost.