Windows Mobile 5.0. Good? .... or Not?

My company has made a deal of some sort with T Mobile UK, so now we are getting some fancy new smart Phones. At the moment we are using HP iPAQ hx2190 Pocket PC's.
The ones we are getting on T Mobile are either the MDA III in grey or the Vario ( i think thats what its called )
Now i like the idea of not having to carry a Phone and a PDA seperatly and having both units in one, but i have no experience of using Windows Mobile 5.0, the units we use now run on Windows 2003 se or something like that.
The thing id like to know is if anyone has any experience with these things, is the reception good? are there any security flaws i need to know about? can i still use e book reader? What the internet conectivity like? That sort of thing.
I know Microsoft are dodgy when it comes to security but the choice wasnt mine the MD decided to do it.
And hes letting us keep the old ones which is nice
Anyone have any experience with these things?