I tried an m601 (automatic) as opposed to a manual m602. The automatic feature on the m601 series is much less reliable than that on an m401 series automatic. I also found flavor to be better on an m401 series than on an m601 (same as an m602 other than being an automatic). I've also tried the m601XL version of an m601, which is supposedly what an m301 apparently is, just named differently (though I'm not 100% sure about that). I found no significant difference between an m601 and an m601XL (which has a sleeved atomizer), other than the cartridge being higher capacity (longer), and the m601XL cartridges also tend to fall off the atomizer rather too easily, plus the m601XL atomizer is less drip friendly due to the sleeved design.
The m601 PCC battery slots are cut to allow for an m602's manually battery switch, so no problem there, but the m601XL sized box has spare cartridge holes that don't allow you to store an assembled XL atomizer/cartridge unit, which is kind of lame in my opinion. Otherwise the PCC box is very much like an m401 series PCC box, other than the charger thread and hole sizes.
The m601/m602 series (XL configurations included) produces very nice volumes of vapor, better than an m401 series, but flavor delivery is noticeably less, which tends to get dissatisfying very quickly. Despite that, since I have the gear, I do use my m601 stuff at home sometimes, but only at home. The m601's automatic feature is so sensitive that it will run constantly in any sort of loud or high frequency vibration environment, such as a night club or in your car driving down the freeway. I've had no problem in that regard with my m402s. The Canadian supplier I used (with very long ship times) was unwilling to take my most overly sensitive m601 battery back. Instead they tried selling me on buying m602 batteries instead, and even a new charger because they said the m601 PCC would not work for an m602! I don't know why they would say that, but they clearly have problems with customer service and also with how they list all their e-cigarette product info at their website. Some information is just plain wrong, or missing key important points. I can't recommend electroniccigz.com as a supplier, and I am only aware of one other supplier in North America (can't remember the name right now) that has much in the way of m601/m602 e-cigarettes and gear.
On the other hand, as a side note, electronic-cigz.com does have Pyramid Tea Bag (PTB) pre-modified refill cartridges (factory e-liquid filled or blank) available for both the m601 and m401 series e-cigarettes, and I do like those cartridges a lot (though they are not quite the innovation equivalent of sliced bread). No one else I know of anywhere (at least on this continent) has those cartridges available, so I guess that is one check mark in electronic-cigz.com's favor. I've never had any problems with their m401 series PTB modified cartridges, which they also have in extra long (XL) size for that model. Those m401 XL cartridges fit just fine on a regular atomizer, no special sleeved atomizer required as is necessary with the m601s (which they don't bother to tell about you on their website).
