To answer in full, need to know if you are doing surface inspection (NDT) or dye and pry.

For both NDT and dye and pry.
Unless you have a microscope with UV/fluorescent lighting, minor penetrations are difficult to see.  A dark booth or room is also required.

If doing dye and pry:
1) The testing is fine, but is often not conclusive,
1a) You can have a part that has solder joint cracks and will still pass die and pry as the part may still be sufficiently bonded to tear the pad or ball (lead) off.
2) Make sure you get all the requisite chemicals including the cleaner.
3) if you have a large part you are testing, the tools may break during removal due to adhesion forces.
4) You must ensure that the dye has fully set (the instructions are clear on required curing times) prior to starting.