I have both the EX and the EXP. Only use the EX on pleasure rides, with essential tool/repair kit + some snacks. I use the EXP to ride to work, but now wish I'd have gotten the DXP, as it obviously has the most storage space overall. I enjoy them both, but knowing what I know now, the DXP would have been the only one I should have gotten, period. So far I've had decent luck with the EXP's fold-out panniers, and outside of the ride to work I don't carry the bag off the bike, so I don't use the shoulder strap or have a hard time setting it down on a level surface. The panniers seem to be durable enough, and with an elastic band on the end of each one, you can tether the panniers' lower ends onto the rack's down-tubing.

As a beginner setup, the Topeak combo has served me well for over a year now...there's no contest between these and a nice set of Ortlieb's...Ortliebs cost more because they're just plain better, but at the point of starting out, I'd say you did just fine in your purchase, and feel free to return the EX for a refund and pay just a little extra for the EXP model.