Almost all IR guns are +/-2ºF or worse never expect it to be better as there are simply too many variables to account for to be certain of better.

Thinks to look for are the DS ratio (distance/spot) and the battery type. The DS ratio describes two things the diameter of the reading area and the optimal distance the gun is designed to be used at.

For example a 1:1 is best used at 4 inches
where a 50:1 is best used at 200 inches, For most keepers a 1:1 or 6:1 is the most valuable.

Batteries I personally like easy to get batteries either AAA AA or standard 9v the button and odd ball ones can be a pain to pick up when needed.