LR attys are notorious for popping out... they are made for more intense heat to the
juice, from the lower voltage units (3.7's)... gotta keep em damp with
juice.
then again there's duds in every batch...
I think you made a good choice in the 2.0 which should be more durable than the 1.5's... maybe Isaac can help you out.
there are less expensive LR 510's out there too. Rob used to recommend EM and he sold them on site for $5. each... try one or two and when you find a good brand, get at least 3,4, or 5 to have backups... they can last months if you treat em right.
IF you get good flavor from LR cartos, then by all means stick with them.
I like joye reg. 510's that are about 2.2 Ohm, no more than that high for the Grand.
You should be looking at attys anywhere from LR's 1.5 to 2.0 Ohm, and reg. from 2.2 to no more than 2.4 Ohm.