The older Sandel HSI's are very good in low light conditions but when the sun gets on to them the unit is sometimes hard to see, it is also practicly useless for instruction as it can't be seen from the right hand seat.
To address the problems Sandel have produced the SN3500 this has a new display and is said to be much better, I will get to see the new unit in a week or so and will let you know what I think.