The DR is a very situational watch; you should only really use it if you need to get past a choke point or if you're running the saharan set. Also, part of being a good DR spy is making your feigns believable (or disguising as a friendly so you don't drop a spy corpse) and getting well enough away from danger so that you can decloak without too much fuss. Used effectively, it can make for a very formidable spy.
The CnD on the other hand is laughable, except when you are using the YER and need to get your first stab, then it's sorta acceptable. Otherwise it is, hands down, the worst watch. The stock invisi watch has a much longer cloak time (seeing as you can pick up ammo to refill it) and doesn't limit your mobility nearly as much as the CnD, thus making it easier to get behind the enemy team quicker.
Edit: also the Pyro was intended as an offensive ambush class, and most people who know what they're doing play him that way. Defensive pyro really just babysits engineer nests.