Well, finally i measured AJA U-TAP vs Blackmagic Ultrastudio Express Thunderbolt.
Used 1280x720p resolution for input-output, built-in Resolume timecode (it's 25fps).
Aja U-TAP gives me 4 to 5 frames delay (0.16-0.2 of a second). Taking photos i admit that i get 4 frames delay more often, so delay is around 0.17 of a second.
Blackmagic gives 1 to 2 frames of delay (0.04-0.08 s). Most of a time 2 frames, so delay is around 0.07 sec.
So, Blackmagic gives 2,25x times less delay.
I am sure that blackmagic keeps delay constant under most heavy load, not sure about AJA U-Tap - will see.
I will not call AJA U-Tap a crap. But i do not like it.
I will keep with blackmagic (thunderbolt and PCIe) - it is fully integrated in Resolume and works better.