That's a good bike at a great price.

The rear suspension is the tried and tested horst link.

I'm not sure who makes the forks for specialized but I've never heard of any complaints about them. Try and find out from the shop/this forum about returns, if any, and spare parts availability. Also check if there are after-market upgrades as well that would work if either you can't immediately get the spares or you feel the need to improve the fork's performance.

Not doing a demo - maybe they've had people skid the tyres out before and/or wreck bikes. Try offering a small safety deposit (10-20% of cost maybe), fully refundable on return of an undamaged bike. Most places in London won't do anything more than 20minutes and even then you've got to leave a valid credit card and one form of id at the shop.

Unless you have particularly unusual proportions I'd just go with the specialized recommended size guide. It worked for me when I was looking at a specialized FS bike.

It's there, ready and you save a bunch of money - what's not to like.

edit: the 20minutes in London can be fudged by going out for consecutive 20minute sessions, i.e., come back after the first 20minutes just to show the bike shop you're not half way to Tijuana/Tombuctoo/far away place.