The two common electric shaver designs work differently enough that one usually suits a given body area better than the other. Knowing which is which saves you buying the wrong tool twice.
How each one cuts
A foil shaver has a straight head with a thin perforated metal screen. Under it, a blade oscillates side to side at high speed. Hair passes through the perforations and is cut level with the screen. The blade never touches your skin.
A rotary shaver has two or three circular heads that spin. Each head has slots that guide hair inward to spinning blades underneath. The heads pivot independently, so they sit against uneven surfaces more easily than a flat foil.
Where foils win
Flat and semi-flat areas: shins, thighs, forearms. A straight head makes even contact across a broad surface, so you cover ground quickly and consistently.
Sensitive skin, anywhere. The screen sits between blade and skin, which removes most of the abrasion that causes stinging. This is the reason foil designs dominate in body shavers marketed for the bikini line.
Short regrowth. Foils cut close to the surface and handle stubble well without needing multiple passes.
Where rotaries win
Curved and awkward areas, if the heads pivot well: the knee, the ankle bone, the contour under the arm. Independent heads can follow a shape a rigid foil skips over.
Longer hair. Rotary slots pull in hair that is longer than a few millimetres more willingly than foil perforations, which can clog.
Dry use on coarse hair. Rotaries generally handle this with fewer passes.
Which for the bikini line
Foil, in most cases. The bikini line is the area where the blade-never-touches-skin property matters most, because trapped regrowth here is what becomes an ingrown hair. Rotary heads cut slightly below the surface, which is the condition ingrown hairs need. If bumps are your main complaint, that difference decides it. There is more on the method in how to shave the bikini line without bumps.
Which for legs
Either works. Foils are faster on the long flat stretches, rotaries handle knees and ankles better. If you want one tool for the whole leg, a foil shaver with a floating head that flexes over contours is the practical compromise.
Which for underarms
Foil, generally. The area is small, the skin is thin, and hair grows in several directions at once. A narrow foil head lets you work in short strokes from multiple angles without pressing.
The honest summary
For a woman shaving legs, underarms and bikini line with one device, a foil shaver with a flexing head is the safer default. Rotaries are excellent tools, but their strengths — long coarse hair, deeply contoured surfaces — describe facial shaving more than body shaving.
The Veloura razor is a foil shaver with a floating head, built for wet or dry use across all three areas.
If your skin reacts easily, electric shaving for sensitive skin covers what a change of design will and will not fix.