Absolutely agree.
IMHO anyone who has a CRD and doesn't have a scan gauge (or equiv) has got rocks in their head.
10 times better insurance against blowing an engine compared to NADS, EGR blocks, catch cans or whatever and they are less than $200, plug straight in and don't void any warranty etc.
By all means block EGR, fit catch cans, chip it or mod it AFTER you get a Scan Gauge.
I'm not saying not too I'm just saying get the priorities right.