I'm 32 and had the ECG - no record of any heart problem so presume it was standard procedure.
No stripping to underpants though just shirt off, and definitely no checking of the undercarriage. Can't see why they would do that - they're looking for things that may affect you when flying so it's not really related?
It does cost a lot of money, but as you say it's good to have a fairly comprehensive health check regardless of the flying aspect.