Anyone who has evaluated Rackspace for pricing would instantly see that Exelion is a tiny fraction of the price for high-end hardware.
Exelion's Basic model includes an incredibly fast Xeon processor, 16 GB of RAM, RAID 1 storage and a gigabit port for $99 per month ($66 per month with 5 year commitment).
Compare that to Rackspace which I'm guessing would charge about $1 billion per month for the same thing although I haven't checked their prices lately. In all seriousness - Rackspace can't come close to their pricing.
Other than that, there are still some open questions - where are they located, how can we be sure they'll still be in business a year from now, or hey, what operating systems they support, etc.