IMO.... Compressed air ABSOLUTLY. Just as Ted said.... once you have it, you'll wonder how you ever lived without it! And pay CLOSE attention to what Bob said about materials for a shop air system...if you intend to do it that way. I've also been in shops when PVC pipe used in the air system exploded, and I had to pick shards of PVC outta myself!
Dust collector system... ABSOLUTLY NO! At least not in the conventional/commercially available type that runs through a piping system, throughout a shop. I have seen a number of knife shops burnt to the ground because of them, and I nearly had the same thing occur. Even if you do have some type of "wet" in the system, or a "spark arrestor", you will forget and the water element will dry up, and if you're willing to bet your shop on a "spark arrestor" you will lose. Mixing in grinding steel, Ti, and various other non-ferric materials and highly flammable other dusts/swarf requires you to think outside the box on "dust collection"
Everybody has their own solution, but I chose a shop vac that runs to a "tray" under each grinder, that can be totally closed off when grinding anything that sparks, also, a 5 gallon bucket of soapy water hangs directly under each grinder. That is the only place in my shop that has dust collection of the conventional type, and it is only on/used for things that do not spark or get hot enough to ignite.
For air filtration, I built/use "box" type filters that consist of old furnace blowers, surrounded by several layers of furnace filters. One I built from scratch, the other was converted from a small swamp cooler.....
You have to understand that the commercially available dust collection systems are designed/built with ONLY woodworking in mind. There are a couple out there designed specifically for metal worker/working, but you are looking at them starting at around $7,500. One of the shop fires I mentioned earlier, was caused when the "spark arrestor" in the $7,500 system failed.
No convincing the world would ever get me to use, or recommend that anyone in a knifemaking shop situation buy/use a commercial dust collection system.
A couple of GOOD shop vacs, and using them wisely, will keep you safer and cost far less then a dust collection system.