I'm using an ASI290MM as a guide camera on theZWO OAG. The small sensor sometimes makes it hard to find a guide star.
A potential improvement for the OAG would be a slightly larger prism. The would allow full use of a larger guide camera such as the ASI174MM. If it were rectangular then it wouldn't penetrate too far into the main camera sensor.
you can use 174 with the current OAG
small prism cause vignetting, but still can have more stars
larger prism is a little hard to compromise with the size of OAG
