Nice little bonus there if they do work. I'd advise removing it for the moment though for the simple reason that it may be related to the cutting out. Not sure of how it's connected, but if it's hard wired or is in between two loom plugs then it may well be a dodgy connection.
That would be a nice easy fix. Also bear in mind that if you were to be involved in any accident the insurance company might use it to wiggle out of any liability if it's not been declared to them (OR if it were still to be found on the car when the assessor looked at it, anyway). Having said that, I would be interested in the make/model of the box if you find it does make a noticeable difference.
Our 163 also feels quick, but I put this wholly down to coming from Citroen 1.9 XUD power
Wouldn't complain if there were to be a few more ponies/MPG to be tapped into though. (average MPG on our S80 manual is 43.2 at the moment, how does that compare to your V70 with the auto and tuning box?)