there is significant degradation of LED life with heat. I know that temperature and life expectancy have been addressed in the Vastex and M&R unit, make sure they are doing something about it too.
Also, find out the wave length of the LEDs as this is a significant factor. Also what is their power rating, at what percentage of full power are they running and in what range of the recommended Voltage are they running. These will all have a very big impact on longevity of the unit.
Finally, you should find a way to confirm the uniformity of the light output at the glass (or even better the screen) level. Vastex has a slight edge over M&R here, but they are both very good. Hot spots or smaller exposure area then advertised could be a problem. My comments go for any unit out there, not just Lawson. . .
You can pick up a UV light meter on ebay for $200 and check the field uniformity for yourself. I would!
pierre