I tell ya, at the prices they offer, there's no reason not to from a cost standpoint. For example, if you want to make a PCB for your booster mods, I think you could go with the 2 layer 5cm x 5cm option for $10. I think standard shipping is $4 if you don't mind waiting on the slow boat from China. That's $1.40 per board shipped which is unheard of.
One thing about PCB fabs is when ordering small quantities, the bulk of the cost is in tooling and setup. So the difference in cost between say 10 boards and 1 board is pretty small. Once you pay for tooling and setup, the number of boards doesn't have much effect on cost until the numbers start getting up there. There's a price point that gives you the best deal for small quantities at around 10 boards. So, that's the number of boards they make for you. Even if it was only 3 boards, the cost would be similar so might as well take the extras.
I'm using a 4 layer board which is typically double the cost and fabs that will do small quantities of them are harder to find. That's why mine are a lot more expensive. Plus, it always goes by board size and mine are 10.5cm x 3.4cm, bigger than you would typically need. A smaller 2 layer board is all you ever need for most projects.
Oh, I just noticed your question. I use Eagle. It has a bit of a learning curve and can be downright frustrating at times, but you need PCB software that can generate Gerber plot files and Excellon drill files. Those are the generic file types that just about all fabricators accept. ExpressPCB software lacks that capability since it's designed to interface only with that particular fabricator. Though, it's a really good free and easy to use program if you just want to print stuff to make your own PCBs using the toner transfer method. If you're a Linux user, cheack out gEDA. I've heard it's really good.
