Upload & Sell: Off
I use the Elinchrom RX and BXRi monos but have considered picking up a couple of D-Lites for backups – they do seem to be a good value. You should also be thinking about what modifiers you may eventually want (softboxes, beauty dish, umbrellas, etc).
As your title suggests, you're very much buying into a "system" and the mounting devices (i.e. the speedring that mounts a softbox to your strobe) are generally unique to the brand - to a degree locking you into that system. Over time you can end up spending more on modifiers than on the strobes themselves and the Eli modifiers are far more expensive than Buff’s.
Buff also has an excellent reputation for customer service and repairs.
Good luck with your decision.