hmmm lots of thoughts on this subject and experiences
you can get a stihl fs 45 for 139.95 and a fs 55 for 199.99 here in tulsa at a mower shop (smith farm and garden) if i was in your shoes thats what i would be looking at.
3 years ago i bought a 200.00 echo from hd, ran good for about 2 months then started losing power, and now after a tune up and even being in the shop it still has a mind of its own and its pretty week.
so this year i went out and droped a 1000.00 on new power equipment. All stihl just like my chainsaw which has never in 5 years let me down.
you asked about combo units and someone said the 4stroke stuff is junk well i bought the 4mix km-110r (head unit) 330.00, the edger 174.00 and the string trimmer 89.00. i also bought the br550 4mix backpack blower. i have used the rest and now im using the best !!! i use this stuff everyday and the 4stroke stuff is awsome. never bogs down, starts quick, quiet, and hardly any vibration. this stuff blows away any other trimmer i have ever used, its just like a 4 stroke you dont have to have it going full bore to work like a 2stroke and i like that.
the one echo purchase i made will be my last, i was reading in another forum about problems with clutches on trimmers from running to much string out or trying to operate a brush blade on one. keep that in mind when you are looking at atachments.
i burned 6 gallons of diesel in my zd326, filled the trimmer up 3 times and the blower up 2. everything went great and working for yourself is all its cracked up to be !!
i have found that not buying the best to start with will cost you more in the long run.