The East River Drive is a great unit. The drive it adds is quite subtle, suitable for use in bluesy rock but cannot deliver highly saturated and distorted tones. It is very responsive to velocity, so if you dial it in right you can have a clean tone which begins to drive if you hit it just a bit harder, very useful for moody solos.
Has the usual EHX build quality in sturdy metal box, very small as well. Three knobs provide all the shaping required.
On the downside there is very little variety of tones available, so would have to be alongside a selection of other pedals in a versatile rig. However since the mini EHX range is competitively priced you can have a few set up together. Also the tone knob doesn't really provide enough variation so would recommend having an equaliser alongside.
On an entirely frivolous note, I love the graphic on the front! Really atmospheric.