What don't you like? I've owned a couple, and I'll admit, the first gen version was a bit portly, with performance that wasn't mind blowing, but I feel like the latest Mtronic version is very good. It's now lighter with better performance. I've never run a 346xp (have never even seen one around here), but have run 550xps, both Mk1 and Mk2. I really like the Mk1, when it is running well. Very light and nimble. Excellent limbing saw. Mk2 has a bit more performance than the 261, according to the dyno, but I can't say I can tell in the real world, trading back and forth. It did gain a pound or better though, for the increased reliability over the Mk1. I've had a v3 Mtronic 261 for about 5 years now, after selling off my OE version. It has a timing bump and base gasket delete. I can't find anything I don't like. Starts well, limbs well, cuts 12" hardwood with ease. I like the Mk2 550 also. I've considered adding one to the stable, but I don't use 50cc saws a ton.