R2a in controlled internal lighting its ok, soon as external lighting added it throws wobblers.
Batterys Duracell last three weeks with around 3hrs total use so plan for it.

Outdoors anything can happen dependant upon light, too much light reads high as much as 30ft/sec, dull can read low around 50ft/sec and give impression rifle not consistent. Also need minimum 7" from muzzle to 1st sensor set on low sensitivity.
These have the RS232 socket not USB, I have a right game getting it to work with pc's. Also continuous problems with rar in XP 32, ok in Win7 32 and 64

R3 much better but like all other led type not immune to lighting and pretty worthless used in uncontrolled environments.
I wouldn't even trust my trusty CED M2 Infra Red outdoors.