Our old PW1730 generator driving two PW1050s has a similar system 
with a warning lamp. It is part of our monthly safety checks to 
verify that no bulb = no HT.
I'd endorse the D5000 recommendation, though we've only had our twin 
goniometer system (general powder and grazing angle options) for a 
couple of months. The software is less intimidating to casual users 
than the Philips equivalent to my mind. But I wouldn't object to a 
X'pert MPD system if it was offered!  A lot depends on your 
applications, now and in the future. And on your funding!
---Graham Patterson       http://www.rdg.ac.uk:80/~slspatte
         Sedimentology: The hard study of soft rocks
*** Opinions expressed are mine unless otherwise stated ***