Use them all the time, never used a treble for three years now. Make them myself with octopus hooks 6/0 or 8/0, braided twine I got off ebay for flying kites (tried builders stuff but melted with heatshrink) and use a swivel instead of those overpriced rings. I would reckon a treble will catch slightly more but on the other hand the assist is easier for bait, doesn't tear holes in the fish and reduces losses a lot (time putting a new rig on over a mark).
When I started using them the hardest part was changing from something tried and tested in the treble, to something new which might not work with the assist. Personal choice for each angler, worth a try and decide what you prefer.