What I notice is that the 510 is good for some people whil the 901s are good for others. It's just a preference issue I think - before the 510 the 901 was king but those who wanted more throat hit weren't satisfied. The 510 was produced for these people... I personally think beginners should start with the 901 as it seems to be more balanced than the 510 in terms of vapor, taste, and throat hit.