I don't use CAD-Duct, but I do use a design to fabrication software for AutoCAD MEP. We have a coil-line duct fab shop here at my company and they can do it all. Before you make this decision you have to ask yourself a few questions first. Trust me, the sales demos look good, but I don't think people realize the time and effort involved.
1. How big is your company? If you're doing $40 million a year or more worth of business, then I can see the justification. If your company is smaller than that, you don't need it.
2. What are the biggest single jobs involving HVAC ductwork you do in dollar amount? If your company does big HVAC jobs ($500,000 and up) then it is worth it. Small jobs just doesn't account for the time involved. It would be a huge time waster.
3. Are you utilizing BIM at all, with weekly 3D spatial coordination meetings with the general contractor? If not, then its kind of a waste. All other major trades that are involved in the BIM process is kind of essential. If not, then you're spending an awful lot of time building a complete 3D model just for your own sake. Then you'll have to request shop drawings from steel, fire protection, electrical contractor, etc just to make sure your 3D model is coordinated with the other trades.
4. Submission of Shop Drawings. CAD-Duct and other programs alike don't really do a good job at creating clean and legible "shop drawings". So you'll wind up drawing twice - once for the fab shop and once for your shop drawing submittal.
Here's my take on the whole "design to fabrication" software. 1st and foremost, it take a LONG time to really get into all the details of the software and set up the parameters that meet the requirements of your fab shop. You have to read through the spec book and find exactly what the job requirements per SMACNA standards. With that information, and AFTER you have all your parameters and preferences set, you then start to layout the ductwork. You are literally rebuilding the entire job piece by piece in 3D. This takes a lot of effort to be this detailed, especially on jobs that are tight fits, or have extra ductwork (for instance, instead of a ducted supply system with plenum return, if you have a job with ducted supply, ducted return, and ducted exhaust, then you'll be out a month transitioning and coordinating each duct run). You honestly would have to hire a full time draftsman to learn the program in and out, and that's all he would do - create each job ready for fab, so he would need to know the ins and outs of the field and fab shop.
It's just more cost effective and much more time efficient to just hand in a written takeoff to the fab shop in most cases. What might take one person two full days to do a written takeoff on a $250,000 HVAC job would take the equivalent of probably up to 2-3 weeks of designing in CAD-Duct. It's just easier to write down "eight joints of 24x18 TDC with 1-1/2" liner" then it is to build it at the exact elevation in the 3D model. You have to think of your taps, your low pressure round, your adjustable elbows, transitions, flat on top/bottom, offsetting duct, any other special fittings, your flex, your duct connections, liner, your elevations, then to fully coordinate it all before it goes in. Too much trouble. It's better to just send a palette of 10" low pressure round duct and let the field put it in per shop drawings, coordinating up and over and around fire protection and sprinkler mains themselves. The field always gives you surprises that the drawings don't tell you.
You just have to be aware that out of all the questions above, if you answer yes to questions 1, 2, and 3, and if you're okay with hiring a full timer to pump out fab drawings to the shop and then create shop drawings separately, then go for it. For big HVAC mechanical subcontractors that runs a fab shop that does big single HVAC jobs, it can be worth it. If your company does NOT have an in house fab shop, then do not use any design to fabrication software. Ever. You're simply doing all the work for them, which is a huge amount of time for not a lot of "discount" through duct manufactures. Sorry for the long post, just thought I'd give you the in and out of how it works from an experienced user. Let me know if you have any other questions.