A couple of small points.
The weight of the thing can become tedious over a long session so judge the alternatives on their weight.
As far as I know, these devices all have a recoil starter - basically a length of string that you pull to start the thing. This is fine when they are new and start first time but gets harder once the machine isn't new. If you haven't got reasonably strong arms, this may be a problem. My wife isn't feeble but cannot start any of our machines this way.
By the way, if these small machines won't start, a can of Easystart (Holts or Bradex) sprayed into the air inlet gets most things (strimmer, chainsaw, generator etc.) going. The spray is mostly ether which can get engines going easily as it burns when compressed in air (like a low pressure diesel engine). A can is worth gold!
If you buy a strimmer, get a protective helmet for using a chainsaw (Stihl, Husqvarna). This has a mask to protect your eyes and ear muffs to protect your hearing. A strimmer may not be as noisy as a chain saw but 20 minutes use will leave you dizzy and deaf. With the helmet, you will be 'fresh as a daisy'!
If you haven't used a strimmer, hire one first to see how you get on. The experience will give you a lot of points to look for and possibly save you money or at least ensure you get a machine that you can work with rather than one you hate.
NN