For £10m I think he is well worth a go.
Like Klaus, I don't think Gnabry will make it here. He has the talent, but I think we will try and loan him out because opportunities will be limited due to who we have ahead of him and the boy needs regular playing time at this level.
As for Zaha, he hasn't really shown what he is capable of. He is very quick and is a decent dribbler if a little erratic. His finishing could do with a lot of work, but the potential is definitely there. Can play centrally or out wide which is what we need as back-up options.
In a way, I think it may be to our advantage that he went to United and then spent time on loan at Cardiff. Had he joined us straight, I doubt he would have been given more than a handful of cup games. Because of the United connection, Solskjaer got him for Cardiff and he actually played a few games so at least he has some experience, however limited, of this level.
£10m is not a lot for a player of his potential and with a significant amount of games behind him at Championship level. He would also qualify as a homegrown player and would be an additional speedy option for our front-line, given how reliant we are on Walcott at times.