The smallest of the range, the Esprit Gemini 125 is suitable for use in a small portrait studio, where you would get around f/5.6, f/8 with a white umbrella at 100 ISO. It is also good as a hairlight or backlight in conjunction with Esprit 250s. There is a single rotary control on the side of the unit. The flash power is fully variable from full to 1/4 but the modelling lamp is fixed at full output.
This model is also useful in larger studios as a top, back or hair light, being triggered from the main flash via the built in photo-cell.