I don't think there's really much to review on them. They're in that top tier of regulators in terms of breathing (IMHO)....but I'm not picky and can't really tell a difference amongst the "good breathers." Compared to (for example) Apeks, Atomic, Hog D3/Zeniths, Dive Rite XTs, and the new Hollis 200LX (or whatever they're called)....they all breathe really well and I can't really tell them apart. That entire list breathes slightly better than the last-gen Hog D1/Classic, DC1/212, and last-gen Dive Rites. The quality on the Deep6 regs is fantastic, the HP port is at a 90* angle to the DIN valve (great for SM mains, imo), the turret is allowed to swivel 360 with hoses attached and they don't run into the handwheel, and they feel high quality. The first stages are sealed diaphragms (my preference) with 5 LP ports and 2 HP ports but there's really little else to say. The biggest difference on these regs (to me) is the "turbo poppet" (or whatever it's called). Deep6 says it makes breathing easier....I'm not sure about that. What I am sure about is there's no way to install it upside-down. Installing the regular poppet upside down can be a huge hassle and even dangerous (if installed just the wrong way). Eliminating that, to me, is huge.
The Downsides: They're new to the game. The risk there is losing parts support for the regs. However, Chris Richardson isn't new to the industry. He got heavily involved at NAUI after being the creator of HOG (under the Edge brand) and has hung around. I think there's little risk of losing him from the industry. I believe Chris said the Deep6 parts kits are interchangeable with the HOG kits, although the Deep6 kits use different materials (for ease of breathing and longevity, per them). So, I really don't see a risk in buying a set. Parts kits are included with regs, as well as their super nice dry box, and first service is on the house.
The upsides are that they're really nice regs, right up there with the best of them and the price is right. I'll be adding a set (or two or three) to my ever-growing inventory. I've done a bunch of try-dives, and I'm getting more and more convinced they'll be a near-future purchase.