I think it's a solution looking for a problem.
For a person, I don't think it would be much use. It could conceivably be handy if the person is away from home a lot, but most of use have family/friends we can trust the see if there is anything important in the mail. They would certainly be a lot more trustworthy than someone in a warehouse who is probably on minimum wage. I certainly wouldn't trust a service like this with important stuff like bank cards, especially as banks insist on posting PINS out (often in the same post, although they are not supposed to for security) to customers. Now, I personally don't think posting PINS is a good idea (much more secure to issue it to the local branch who can then ask for ID to release it), but introducing a third party like this is opening security a little too much.
It could be more use to small companies where the staff may be away from the office a lot. Although they may be better off with a complete commercial answering service which would include human operators for the phones and a mail pick up service.
Would I trust it personally? No? Basically because, beyond the fact that the site is asking me to redirect my most personal mail to this company, I know NOTHING about the company.
It's also worth noting that the security accreditations they list are worthless. Not because they are bad organisations, but because they have provided graphics and no link to an independent site where you can verify them. It's also suspicious that of the two names I recognise, neither are known security companies. Swann manufactures hardware of various kinds (although security cameras are one of the things they manufacture) and the CRB checks criminal records.
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It's also slightly worrying that the website of the system that powers their service, iPostalMail was apparently created on 21st August 2009 and never completed.
http://www.ipostalmail.net/