Yup... You're right, the Echo is probably heavier than an equivalent gas trimmer. For me the deciding factor was that I could use the battery in other Echo products, without having to buy more batteries, just purchase the bare tool.
Also, I've no idea how big the OP's property is.. I took the " not too heavy" as meaning that the property was large, and a heavy unit was tiring to lug around for an extended time. Duh.. I should've asked how long it took to trim, and that would have given a better idea of the what level of unit is required.
Only other point would then have been the warrantee .. I know the Echo stuff is 5 years consumer, which speaks well of their faith in the build quality of the product. If any other brand will do the property on one charge, and has a 5 year warrantee, pick the one that feels the best when you're using it. Sometimes, "heavy" can mean unbalanced, or, in need of a properly adjusted shoulder strap.
I'd suggest get one from Home depot, take it home and test it out. If it's not right for the job, take it back and get something different. Repeat as necessary until satisfied.