I've got one of each. The older Svea burns hotter, bigger more aggressive flame. The self cleaner 123 model....is easier to clean. Both have been 100% reliable.
The wicks only need to be replaced if you run one dry several times. When the wicks dry out and cook, they caramelize and won't 'wick' anymore. My wicks have never been replaced and work fine. I've also got an R8 Hunter that shares some of the same parts and is also a great car camper stove....too heavy for packing.
MRS stoves are good stoves. They work very well but I had problems with plastic parts. My favorite pumper stove is an Optimus Nova which a wonderfully reliable stove, no plastic parts. I'd just like to see Optimus come up with a modernized Svea, Ti or Aluminum, with an R8 style tank but removable. A self pressurizing stove design, like the older Optimus's would eliminate a third of a stoves weight. Brass and silver solder is what makes Sveas un-ultralite.
I've also got a Coleman Peak I, bought back in the early 80's. It's now unusable...pump parts are siezed/rotten and the generator requires a break-over bar to remove and clean. It's been retired.
All things considered the old Optimus pumpless stoves have required zero maintenance, work every time, and are older than all my other stoves combined.
No plastic and the only washer/seal in the things are made of carbon...except the cap gaskets. Come to think of it, I replaced one, once. <img src="/forums/images/graemlins/cool.gif" alt="" />
I guess that's why I use Esbit/cookfires/alchy stoves now...... <img src="/forums/images/graemlins/grin.gif" alt="" />