We've been using the SMC base mount and solenoid valves ( sold
here by vex ) the last 3 years and the only problems we've had with them is that the mount's exhaust will leak if a valve is not screwed in all the way but it's an easy fix.
With a single solenoid valve costing $50 and $70 for a double they might be more than you'd be willing to spend since it's just demoing. But if it's something you plan on using for the next few years then I'd say they are definitely worth the price as they hold up really well and don't seem to get affected much by age/usage.