Probes are like different modalities-- many opinions about what's best, but little consensus. The main thing is still operator skill.
Insulated are probably a bit safer, especially with blend and galvanic.
Bulbous probes appear to concentrate the energy at the base of the needle, which may assist with effectiveness. As you note, they also may be less likely to push through the bottom of the follicle.
Other things to look for are disposable probes (a must!). Some prefer gold needles because of metal allergies.
Again, operator skill is more important than probe type. Hairfacts: Electrolysis probe manufacturers