The keycaps you can typically buy for MX switches are universal, they will fit any MX switch with any stabilisers, the stabilisers just differ in their mechanism, the way they "interface" with the keycap is the same.
This is a Cherry stabiliser on a spacebar, as you can see it has the 3 distinct points to connect to the keycap.
Below is a Costar spacebar stabiliser
with Costar stabilisers the bar is visible and connects to two of the inserts pictured below, which then slot into the switch in the same way as the Cherry stabilisers.
Basically Costar stabilisers have visible bars, Cherry do not.
Cherry have the advantage that the large keycaps are easier to fit as you just have to push them down, whereas with Costar the large keys have to be carefully slipped on. This is because with Costar, the white stabiliser inserts usually stay connected to the switch when you remove the keycap, so to put the keycap back on you have to thread the loops of the stabiliser inserts over the ends of the stabiliser bar, and then push the keycap down.Cherry vs Costar (Click to show)
Note: This is not a conclusive comparison, just what I have learnt so far, feel free to correct me if I am wrong on any points. CherryPro's:
- Easy to take keycaps off/ put back on
- Don't have to worry about breaking the loops of the stabiliser inserts as much
- Occasionally a "tinny" sound
- Easy to break the stabiliser inserts if you're not careful
- More difficult to add/ remove
AFAIK the Trigger has the standard US layout, so you shouldn't have any compatibility problems with US layout keycaps.