Before the Elinchrom ELB 500 was announced, I had a set of Ranger Quadra ELB 400.
It is a great portable system both in that it uses battery power and is incredibly small.
I generally prefer the ELB 500 for the increase in power (light power and battery power) and TTL features but I still use the ELB 400 from time to time.

Be careful to note which head type you are buying.
I bought my set used from BorrowLenses.com and it had two different style heads. None are bad and they all work together but have different use cases:
Pro: General
Action: Short Flash Duration to freeze movement
HS: Designed for High Speed Sync to more easily overpower the sun by being able to use shutter speeds of up to 1/8000 instead of the traditional 1/250
Shop on Amazon - One Pro Head
Shop on Amazon - Two Action Heads Kit