Jim, you sold one to me which I use in my Lynx B Vintage formula vee.
For the price it is tough to beat if you want both GPS data and vehicle data at a reasonable price.
The good points.
1) GPS ability requires no beacon and gives you speed position and elevation every place around the track.
2) The display is completely configurable - meaning that you can change position and font size of every parameter.
3) The lap timer function is typically quite accurate.
4) The input parameters are fairly flexible allowing a number of different options for sensors and inputs. if you do not know the parameters of the sensors you will need to calibrate them before using. XT is now offering their own line of sensors which may simplify things a little.
5) You can review the track map and look at your speeds right on the dashboard of the session. It may also display other parameters such as rpm - I will have to check.
6) The unit is tiny and will suface mount on a dash so is good for big drivers such as myself which need lots of leg room.
7) You can save up to four vehicle / driver configurations on the unit and move it to different vehicles easily.
Unit is pretty easy to calibrate and set up.
9) Accelerometer data seems to be pretty smooth and accurate
10) Unit is self powerd if needed , light and portable, Can also be used to track acceleration runs. I even used it to log the acceleration and top speed of my dog - this was probably not the intended use. Dog performance data available on request
The bad points
1) GPS resolution is only 5hz - units such as the AIM solo are 10hz
2) Analysis software is basic and does not allow same level of comparison / optimization as AIM software.
3) Analysis software does not support math chanels - you can dump time series data into an excel flat file for analysis if needed.
4) Early units hatd a plastic case with an internal GPS antenna - durability is ok - later units had an aluminum case but an external gps antenna which is slightly more difficult to package in a formula car.