I'm familiar with ExpressPCB. There is a huge catch22 with this service.
For a professional, the price could be reasonable. Shipping is fast. Ordering is easy. Don't even need to make Gerbers. Just click and done.
But a professional would not suffer the limited software. Can't do more than two layers. Can't alter paste layer. Can't make a bottom layer silkscreen. List goes on. ExpressPCB software is excellent for one thing. It is very easy to make simple boards with it, without making new device footprints or schematics. It has tools for simply designing the entire copper layer straight off the bat.
And a professional might need hundreds/thousands of boards after the prototype is tested. For higher quantity, the price just gets worse.
Designing a board in a closed software that can't make gerbers is just a waste of time, unless that software and manufacturing service are simply excellent. This is not the case with either.
So the only thing Express PCB is good for is a hobbyist with money to burn and who finds their software easy to use. For one-offs, 2 day shipping, and one click ordering, the price isn't super terrible. I'd continue to use them while learning a new pcb software, pronto. You may also want to learn how to make your own boards, using photoresist or toner transfer. The only easy alternative manufacturer is yourself. And of course you will continue to use their service in the interim. You don't have any other choice!
ExpressPCB is a useful concept. It's a little like PICAXE of the PCB design/manufacturing world. Super simple, but you pay a premium and will not find it terribly useful beyond proof of concept of simple designs.