The wedge-type (Aloris BXA) is far superior to the push type (Aloris BX) toolpost.
The wedge-type tool post has two distinct advantages:
1) The front dovetail (toward the spindle) is fixed; it does not move. So the reference which it provides does not move. The wedge pulls the tool holder forcefully into this dovetail. This locates the holder on the X and Y axes quite accurately.
2) By virtue of the dovetail geometry, the wedge pulls the holder back against the body of the post, so the full width of the holder wings bears against the post body, forcing the holder rigidly square to the tool post, preventing rotation about the vertical axis.
By comparison, the push-type has no rotational reference at all. The holder will rotate depending on exactly where and how the two dovetails mate between the holder and post.
In the X and Y axes, the push-type post relies on the mesh of the dovetails, but without providing any reference for that mesh. The holder is a loose fit on the dovetail, as is required to mount and dismount it. Therefore, the exact position of the holder WRT the post is variable.
I have a BXA (real Aloris) on my Monarch 10ee and have seen no measurable error in tool position. Of course this is predicated on keeping everything very clean. Any little bit of swarf can throw you off.
Use a real BXA (wedge type by definition) and you'll never use anything else.
