Provari = battery, REO = battery + juice (3 or 6 ml)
Provari (18490): ≈ 1" diameter x 4.1"H + tank height
REO (18490): ≈ 1.7"W x 1" deep x 3.1"H + atomizer height
IOW, Provari narrower, REO shorter
Cartomizers (approx 1 ml capacity)
REO - carto can be used standalone and/or replenished by 3 or 6 ml internal juice bottle
Provari - carto can be used standalone or be punched or slotted to accommodate a slip-on carto tank
Atomizers
REO - disposable or rebuildable drip atomizer fed by 3 or 6 ml internal juice bottle. Tank type usable with adapter (not fed from internal bottle), but redundant.
Provari - disposable or rebuildable drip atomizer manually dripped. Can also be used with a tank type rebuildable atomizer.
Clearomizers
REO - use possible with adapter (not fed from internal bottle) but redundant.
Provari - 510 style works natively, eGo style requires adapter
Provari (18490): ≈ 1" diameter x 4.1"H + tank height
REO (18490): ≈ 1.7"W x 1" deep x 3.1"H + atomizer height
IOW, Provari narrower, REO shorter
Cartomizers (approx 1 ml capacity)
REO - carto can be used standalone and/or replenished by 3 or 6 ml internal juice bottle
Provari - carto can be used standalone or be punched or slotted to accommodate a slip-on carto tank
Atomizers
REO - disposable or rebuildable drip atomizer fed by 3 or 6 ml internal juice bottle. Tank type usable with adapter (not fed from internal bottle), but redundant.
Provari - disposable or rebuildable drip atomizer manually dripped. Can also be used with a tank type rebuildable atomizer.
Clearomizers
REO - use possible with adapter (not fed from internal bottle) but redundant.
Provari - 510 style works natively, eGo style requires adapter