:: Security - Presumably if the 'control' server is compromised, you're going to have serious problems.
Basically yes - although as recommended you do not have web etc setup on the same box, ie no client user accounts etc - our CP box just runs the CP and DNS2
:: Stability - How well tested is it (compared to cPanel for instance)?
I have no experience with cPanel so cannot comment on that (Cue Karl
) But H-Sphere is extremely stable.
:: Integration - How well does it integrate with Worldpay, especially with regard to recurring payments?
Actually I have to say here, not as well as you would hope, we currently use WP with H-Sphere, but it does not take advantage of FuturePay at all, for recurring payments an email invoice is sent out with a link in that the client must manually make payment from (via WorldPay) This is actually one of the main reasons we are just about to move away from WP