No, it's not a trickle charger.
An EchoCharge is a specialized device (currently built by Xantrex) which is used to keep a starting battery topped off. It works by sensing a charge on the house batteries. Whenever the voltage goes above about 12.8VDC, it bleeds off some of the charging current
from the house batteries (up to 15A maximum) and uses that to charge the starting battery. It will not overcharge the battery and can be left online all the time. I've had one installed for several years and love it.
Here's a brief description: EchoCharge
They cost about $100, and are well worth it.
By the way, they work with ANY charging source: generator, shore-powered battery charger, engine alternator
, solar panels
, wind generator
, etc. All they care about is sensing a charge on the house batteries. When the house battery voltage drops below about 12.8, they disconnect until the next time a charging voltage is put on the house batteries.