This. I like it fine out back, but much prefer a Minion or several other options on the front. I think kidwoo posted a pretty good treatise somewhere (HR2 thread maybe?) on the DH forums explaining why a HR up front is weird - even if some WC guys ran that it way.
for a trail bike, i dont see why not.
for a downhill bike, the hr up front is too unpredictable. it has this weird transition when leaning, where traction is iffy. and when it get loose, it just goes; without any previous hint.
having said that; some really fast guys i know have hr front and rear. but they lean and carve harder than most people have the skills for.
Something else to consider is that the UST 2.35 Highrollers only come in 70A rubber compound, which is slightly softer than granite. I ran those front and rear for a while, they never wore down but traction was a bit iffy in the wet.
I'm currently running a 2.5 exo Minion setup tubeless up front and like it quite a bit. Only a slightly heavier than the 2.35 UST Highroller but far grippier.
If you weren't referring to the UST Highroller, disregard my comments.
I've got 2.35 High Rollers on my trail/xc bike rear and front, love them. Very predictable tire at high speed and angled as well, confidence inspiring. Worth the extra cost over cheaper tires.
Only trade off I've noticed is that its a heavier tire with higher rolling resistance than what I replaced them with, but I feel the positives certainly outweigh the negatives for me. I'm sure others will feel differently.