I get this a lot from customers, here's the skinny:
The M55 is a very large BTU stove, runs quieter on a low heat setting (no pellet dropping sound) but the M55 relies largely on convection for heat transfer. It has a better heat exchanger. IF you remove the fuel restriction plate in the hopper you could get up to 77,000 BTU's but you have to relocate the high limit switch.
Actually, the pellets dropping into the burn pot are about all I hear when in a low setting. Even at heat level #4, it is much quieter than the Accentra. I was able to compare the two stoves side by side, both operational and running. I would not recommend removing the restriction plate, there was a good reason Enviro put it in, and it had to do with the hopper getting very hot when running the stove in higher heat settings and the high limit switch would trip. You are suggesting that M55 owners reconfigure their stoves in such a way that it could be unsafe to operate.
The Harman Accentra, like all Harman Stoves, shares the heat transfer in both radiant and convection. Harman Stoves have the ability to run with the room fan down to almost off...which makes the much quieter on higher heat settings. Harman Stoves are easier to use, slide out, pick up, clean and maintain.
I can't speak for the Harman stove having a radiant effect but I can say that the M55 is very easy to slide out of fire place opening and clean and maintain. There are 4 pieces that I remove in order to do a very through cleaning of the burn chamber and they are not difficult to remove or reinstall.
I want to be a fan of the m55 but there are things about that stove that bother me. Anyone new to pellets that gets this stove has issues to get over the learning curve...it just has too many options. IMHO, many dealers do a poor job of teaching the principles of combustion to stove owners, this is the root of most needless service calls.
I am new to pellets, I did about 6 months worth of research and visited as many stove shops as possible before I bought the M55. I even read the user manuals of the stoves that I was interested in before I went to look at them so I had a better understanding of their operation. The M55 does have many options, however, a proper installation should yield a stove that only needs to be set to the desired run mode (manual, Hi/Lo/, Auto/Off). I found that the Accentra had just as many operating modes and options as the M55, but with the M55 I could hook up a t-stat for regulation and this made more sense to me and better fit my requirements for a stove. Yes, it is up to the dealer to educate customers on the products that they sell, but it is also up to the consumer to educate themselves first. You can't blame the dealer for a consumers negligence in stove instillation and maintenance.
Harman stoves allow pyrolysis to happen in a very natural way (top down), therefore the stove becomes somewhat "hands off" for operation. the M55 is very much "hand on".
Other then adding pellets and doing the required cleaning, I feel that my M55 is pretty much "hands off". The hopper is full, the t-stat is set, the house is warm. No problems.
I'd take an Accentra over an M55 any day.