That foal is seriously cute the mare OK, I like her.
I would however ponder on the following.
10 years old, bred 4 foals. That doesn't leave that much time for being a riding horse and here we are lame with ringbone (do you want a lame horse round the place?).
She is shod in the photo - odd for a broodmare, unless they tried bringing her back in to work and she went lame I guess.
£400 ono is highly tempting, but sometimes cheap horses aren't that cheap in the long run.
For me, personal opinion only, it would depend what stallion you are crossing with, she is already a mix.
What would be your plan for her? Breeding or companion? Looks a lovely sort but hind legs look a little oddly angled. That could well be down to the ringbone though. Trying to take pressure off? Lovely conformation apart from that.
Seems strange for a broodmare to be trimmed up and shod. I don't think it is a good idea to breed from a broken down mare either, doesn't instal me with confidence in the soundness of her offspring (lameness through injury is a different matter)
To breed from? no mention of any noteable worthy pedigree, no competition/ridden record herself? Not to mention ringbone, The horse market is already flooded and quality well bred youngstock isn't selling, need I say more?!
Added to that surely the excess weight of pregnancy will increase the level of pain from the ringbone??