If the pumps high pressure generation is suspect then there are alot of tests that need to be done before replacing the pump.

Cranking the engine for five seconds while watching live data would not give me enough confidence to spend £1200 of my customers money.

check
supply quality and pressures
leak off
cranking speed
Just for starters

I would think if the vehicle starts efficiently hot/cold fuel pressure may not be your issue, but does need eliminating anyway.

hth
James