Hi Gary,
Accuracy really isn't going to change any at all between the three that we carry.
The premium blue refract is a little more sturdy than what the ASICO refract is. This is by far our most popular unit. For the money it is pretty hard to beat.
If you are going to be using your refract multiple times per week then i would recommend the Sybon, as it is more "heavy duty" than any of the other refracts out there. At $60 it's a bargain when compared to others identical or cheaper made than it at $100 - $150.
If you are going to be using