UVB meters are relatively inexpensive and easy to use. I would recommend any agamid keepers obtain one.
I've hundreds of UV tubes in the last couple of years and did quite a bit of testing in that time. In general, zoomed tubes produce the highest amount of UV. Exoterra and NEC blacklights are a little behind. In recent testing, zoomed 10.0 produces approximately double that of zoomed 5.0, which in turn produces about double as much as an NEC blacklight.
My recommendation is if you are going to use tubes, go a 10.0 and don't bother with 2.0 or 5.0 tubes. Even then, always makes sure your dragon can bask within 30cm or so of the tube.