I just finished building a CNC machine and I used NSK linear actuators. I also have Misumi and THK linear actuators here ready for my next build.
In terms of suitability for a CNC project, it really depends on the specific actuator. They come in all shapes and sizes and some are better than others. More specifically, you need to ask what type and size of linear rails they have inside, the number of bearing blocks and the size and pitch of the ballscrew as well as the grade.
Some actuators use a belt drive instead of a ballscrew. These should be avoided. Also avoid any with just one rail or just one bearing block on each rail.
If you can find a set of actuators in the specs you need, they are a great time saver. The rail, ballscrew and table mounting will be significantly better than what most people could achieve with a diy actuator. A lot of them come with tapped mounting holes which again, are more precise than I could do myself. Most of them come with an enclosure which is great for avoiding chips getting into your rails and ballscrews. It saves you buying horrifically expensive bellows too.
If you get lucky, you can sometimes find them with a set of pre-made (and super accurate) mounting plates to join two actuators. This would be a huge advantage when trying to make everything square and parallel etc. They are often sold in 3 or 4 axis sets on eBay as Cartesian Robots which is a great start for a CNC router build.
The NSK actuators I used came with 25mm square NSK rails and 20mm c3 ballscrews with a 20mm pitch. I only just started testing my machine with aluminum milling but, so far, they have performed extremely well. The only limitations I have run up against have been related to work holding and tool breakage. The actuators all run silky smooth and quiet.
I should add though, that I spent a lot of time and effort building a very solid (and heavy) machine base to mount my actuators on. My gantry is over 8" thick before I mount the actuators. I would not advise building a CNC machine using only actuators without a sold base. Also, you will probably need two actuators for the Y axis unless you have a very small table. They typically have the rails mounted much closer together than what you see with moving tables on diy CNC machines. If you are building a moving gantry machine, you will definately need to buy 4 actuators.