Are you getting the original MKI or the one TW sells which is the MKII? I only ask because you say you are getting adapters to go from 901 to 510 and the original MKI is available as a 510 model if purchased from their site in the UK.
The MKI rocks IMO and is my goto device. I have a few different PV's and right now the "precious -L" is my favorite, but I always seem to go back to the SD MKI. Size, reliability, weight, simplicity. It is not a HV device however. I have used LR atomizers and though they are OK, I find a good regular atty running on a big battery mod w/ a 18650 more to my liking. The LR works great on the SD though to "simulate" HV. I have HV mods also, and honestly, I think they are not worth the hassle as compared to a good 3.7 device w/ a good LR or standard atty.
To answer your question directly. LR atomizers have lower resistance, therefore the current through them is higher and the heat produced is also greater. Downfalls: Possibly shorter battery life and atty life. HV atomizers have higher resistance and are designed to be used with HV mods, though I don't see the point. You only "need" regular atomizers. LR atomizers would be the route to take vice a HV mod IMO. It is certainly cheaper.