I haven't had any experience with the 601 but I do like the 401. This is what I've written about it in the past
M401/3 ~ This is a strange little PV. I have the 401 with manual
batteries and also have a few 403 auto batteries because the smaller 403 batteries make stealth
vaping, when necessary, a lot easier. The 401 has a very small cartridge. It holds less than .5ml of liquid but it wicks so well you get ALL of the liquid and refills aren't needed as often. When home I use a contact lens case to dip. One dip will give me about 30 minutes of chain
vaping.I've had my 401 for several months and I've only lost one atty so far.