We spend a lot of time in Chipping Campden and know the Northern Cotswolds very well.
Aston Magna is a hamlet really, very tiny, only houses. We've driven through several times (we have friends who live nearby in another tiny hamlet), and the roads in that area are very very narrow lanes. You wouldn't be far (less than 10 minutes drive) from Moreton-in-Marsh, a bit further to Chipping Campden.
I'd personally prefer to base somewhere just a bit bigger, at least with a pub, where you can be a part of village life without having to always drive everywhere. You'd find some sort of village shop very handy as well. We love Chipping Campden and will be back there this summer for a month. We've rented in other villages and also done several walking trips in the area. The walking is outstanding.
The cottage does look nice. I especially like that outdoor area. I don't know the agency, but the website is well done and they seem to have many nice properties. The lack of reviews doesn't personally bother me, but you could write and ask them about this. Maybe it is a new listing? Or maybe they can give you some references.
I can personally recommend these two agency with lots of rentals in Chipping Campden:
http://www.honeypotcottages.co.uk/ and
http://www.campdencottages.co.uk/. I have always wanted to rent this cottage
http://www.honeypotcottages.co.uk/little-orchard/ that was once the home of Graham Greene, but it's a bit more than we need for just my husband and me and on the wrong end of the village for where we need to be when we're there with our groups. I don't know if this would suit you...
Anyway, just my thoughts. I know you will love the Cotswolds.