I have one and I love it. In fact, I just had Steve Gamble install a pee-valve as I spend a little too much time in my D1! The liner is unquestionably hard on bare skin, but abrasive isn't really the best word choice, it's more akin to being waffled by the 3D-mesh print. The liner is not permanent attached and can be very quickly removed (think a couple zippers and Velcro) if it's not desired for the particular dive. It's also a benefit to wash the liner and we've found that it is a durable material capable of easily surviving a standard washing machine.
The D1 comes with user replaceable silicone seals (neck and wrist) that are genuinely replaceable anywhere but underwater! The addition of dry gloves is also very easily user installed. You carefully remove the existing oval-shaped ring system (theoretically no tools required) and transfer the existing seal to the new wider ring. (The larger ring is required to mate the press-on dry glove) Once you make that simple swap the dry gloves literally click into place and do not require the removal of the wrist seal or ring system to install.
The D1 comes with two expandable thigh pockets. I don't know why you'd need to expand these pockets as I'm able to carry just about all my backup cave gear in those pockets without expanding them. The pockets easily swallow four spools, a backup mask, slates, scissors, and my backup lights. Speaking of cave diving, I also like the zip on/removable wrist seal covers featured on the arms of the D1. The removable wrist covers protect the entire wrist seal and overlay the gauntlet of wet gloves nicely. If you're wreck or cave diving this is a feature you might want to consider. The neck seal has a similar fabric cover which very clearly aids heat retention and performs a nice job holding onto wayward hood bibs. The wrist seal covers, neck seal cover, and pockets make for an incredibly clean configuration which makes for a very clean look in underwater photos. You can really look squared away just by hiding and covering things!
Fundamentally, the D1 with the liner installed is a Thermos. Your body will heat the air in the suit, period. You should very carefully consider just how much undergarment you're applying for a particular dive. My personal observation is that I can wear exactly half the undergarment of what I use in my Bare Trilam. Some divers (myself included) find wearing too much snowsuit as a real disadvantage in terms of ability to reach across our bodies to active things like OPVs, Manual Add Valves on rebreathers, etc. The liner is infinitely pliable and will contort in whatever shape far beyond what my 400gram undies will allow!
What I've done is pair the suit with the lightest Waterproof BodyTec undergarment (200gram) with no problem in water as cold as 47 degrees for exposures exceeding an hour. The dealer catalog has a warning about the 400 gram undergarments not being appropriate unless you're in water approaching 32 degrees. The liner adds value in not obvious ways though - decompression. When you're lying on your stomach for an hour watching the blue world I've noted the air in a typical dry suit tends to migrate to my back. This tendency means that the suit is very close to the front of my body as the air is all crushed out of the undergarment. Anyone who's spent any real time hanging knows this promotes core cooling of your body. The D1 essentially solves this entire problem as the water is always a constant distance away. Giving your body the opportunity to heat the space and maintaining the space absolutely makes deco a warmer experience across your entire body. Another hidden advantage to the liner is pee valve users will note the hose is generally not crushed against your body during deco. I'll let you figure that part out for yourself!
Clearly there’s no free lunch with this air space, you might need to add about 5-6 pounds to your configuration and some divers report feeling a bit fin light as there is more air in the legs than they would otherwise plan to use. Whether this is a disadvantage of inherent trim, or an advantage as you’ll now keep your legs warmer is a personal debate.
For my money, the D1 Hybrid is a brilliant suit. The D1 is rugged, can be configured and repaired by the user even when it’s wet, and the option of diving it with our without the liner makes for an all-around winner in my opinion.
