The DVO Topaz is more comparable to the Mara Pro with the external bladder, but you won't need the bladder if you're not really moving that suspension back and forth. You'll get great parts/customer support with either DVO or Manitou, but the Mezzer Pro is a fork made for some serious trails. IIRC both DVO and Manitou sell every single part for their stuff so you can do a complete rebuild no matter what, and with Manitou (more than likely DVO as well) you can swap in compatible upgrade parts.
When I was speaking to Dougal at Shockcraft about getting the IRT upgrade and high-flow damper valve for my Mastodon Pro he told me that his high flow damper valve works so well Manitou copied the design for the Mezzer Pro as of MY2021+, so in effect my Mastodon Pro is now a Mezzer Pro with fatbike spacing (and 34mm stanchions instead of 37mm, but no biggie since I'm not fat and I'm too scared to ride black trails)
Reading up on the DVO fork it looks like the OTT feature is similar to the Manitou IRT in what it does for the rider. The IRT just replaces the volume spacers with a 3rd air chamber (the 2nd is negative self-balancing with the 1st) and allows to you run a much lower pressue in the main chamber, for better small bump compliance and a more tunable progressive rate. The OTT seems like an independent (from the main chamber) preload on the negative chamber with less adjustment (3 points vs 'infinite rate' of air pressure) - but being a coil spring would probably have better small bump absorption and less stiction - so the main benefit of a coil fork with the lower weight and better adjustability/progressive rate of an air spring (with the main chamber and volume adjustment via fork fluid).
@kwseattle where did they have you add the oil? Pretty cool they can do that to reduce the volume in the air spring in lieu of spacers, gives you a finer adjustability than volume spacers - and it doesn't look like you need any special tools other than the vise grips? The Manitou fork requires a $60 set of bits for service, but at least the split spline thingy is the same as a cassette removal tool.
In the Topaz it's just the little volume spacer rings in the negative & positive chambers but very easy to add, then setting the bladder pressure and chamber pressure, then the little knob.
TL;DR go with the DVO option as the rear shock is better and the Manitou fork is probably overkill. I bet the DVO fork can get as comfy as the Manitou in your situation and may even be better at higher speeds on smoother trails thanks to the coil in the OTT - that feature just isn't as easily as adjusted as the IRT but should be more of a set and forget since coils aren't affected by air temp and heat buildup like cair springs are. Spend that price difference on carbon bars and accessories - carbon bars help a lot with vibrations and save a little weight.
) and lifted it up to find that there was nowhere for me to add oil. Reached back out to DVO and he mentioned that I need to remove the core of the valve and add it in there, and "make sure you put at least 100psi in the cartridge before tightening the top cap back up. You want the fork to be at full extension so there is no negative air pressure in the lowers" which I absolutely did not do when putting it back together (oops). I'll take it back apart this weekend when my valve core remover tool arrives. I'll have to use a syringe to get the oil in there, which is fine because I've actually got a bunch of broad needled syringes for cleaning fountain pens.
