Personally i wouldnt go with SL1. Its USB 1.1 meaning high latency, only supports 2 decks (if you want to upgrade to 3 decks at any point you'll have to get SL3.
SL2 is definately better than SL1 but to be honest, if i were you i'd grab SL3 on ebay or something. Or if your stuck for cash hop on djfinance.