OKies lets see. Bear in mind I am 5'9 here.
Firstly, for a pool to be of use you need to be able to immerse your bump and back in the water so as to help the pain.
In the £14 pool I was able to do this when sitting down in it and then also when I lifted my legs up and bent them so I kind of floated a bit on my back. My bump and back were not covered when I knelt. When I was on all fours, only my bump was in the water. I also tried being on my front with my arms over the side and head resting on the side also and then bending my legs so I floated kind of. Hope you can kind of get the picture there
Now, I was fine labouring in the pool and had I not gotten simply too tired and lost my contractions I may well have delivered in the pool anyways. As it was, because I needed to change position and also get moving I got out.
Depending on how you cope when it comes to the pushing stage is the thing. If you need to bear down to push you may prefer to be more upright, say kneeling. At this time I found the pain (out of water also) far less than the first stage of contractions. Kneeling in the pool and having baby would probably have worked fine for me as baby would have been under water. Bump would not have been.
All in all, 5'7 I'd think the £14 pool would be ok. Just be prepared if you change position to kneeling or squatting when pushing baby out to not have bump and back in water. But as I said at that point in labour I don't think it matters as much as during the first stage when just having to bear with the contractions and not push.
Also FWIW we bought a pump to inflate the pool. Did it in 15 minutes. Then we bought some plastic hose to attach to the shower and run through into the sitting room and fill the pool. OH also used a couple of buckets and filled from the tap also. Took about 30-40 minutes to fill to a decent depth and I could get in. Was then topped up.
To empty it he put the hose back in and sucked on it to get the water flow going back the other way. And also used buckets to help it along. We put some of the plastic sheeting over it in place of a proper cover when not in use and to keep it warm. Then took out a few buckets of water and replaced with hot when needed.
I'd save your pennies on all the fancy pool kit to fill and empty etc and go the budget route if you can. For a single use its a daft amount of money to spend.
Birthpool in a box is good as I understand it. But the £14 pool does the same job. It was really solid and I loved it. And had I not been worn out I'm sure I'd have pushed LO out in it. Position wise I laboured first stage great in there. Very comfy.
I'd recommend getting the £14 one anyways. Then go to a DIY store and finding the bits and bobs to help fill and empty. If you feel you need the kit (pump, cover etc) to do so then order just that from the birthpool site perhaps? I'd personally not bother but its up to you.
Hope that helps