$5 for an Earthway S15! You should almost get arrested for that - it's that much of a steal!
I have one and like it for certain spraying tasks. It is awesome for spreading Serenade as part of a proactive fungicide program.
I have yet to use it for anything requiring very precise distribution. I plan to use if for spraying glyphosate on my front lawn in a few weeks...
I had one and was not a fan. Pain to push and if you accidentally go backwards with it, it is toast because of the pump.
The S15 should go backwards just fine - the manual actually recommends pulling it backwards for transport.
What you need to avoid doing is going forwards with it when it is empty -- that is what damages the pump and is warned against in the owner's manual.
I'm still aghast at the $5 price. I would have bought all of them at that price, and just used had one for every different lawn chemical to spray!