In my opinion, well worth it for the added comfort provided by the extra heat control.

Of course I DIY...so it cost me probably $40 in extra materials and a couple hours of my time. Since you're having yours done for you, I'm not sure what they're charging you...or what kind of materials they intend to use...or their workmanship or the type of workmanship you are expecting. Honestly the sky is the limit on this sort of thing, and there are too many variables and opinions to give you a real straight answer.