Thats a current opperated ELCB, aka an RCD, its rated correctly for additonal protection (0.03A = 30mA), as long as it tests out its still compliant. The ELCBs you should watch out for are the old voltage operated ELCBs usually found on TT systems to provide fault protection, as they can be easily rendered inoperative and fell out of use i the 80s for that reason, so any out there will be quite old now, and may stat to have mechanical issues, in addition.
There was a VOELCB insalled here but it failed to operate:
https://www.youtube.com/watch?v=cYj55s0ENdY but it faild to operate (This is in an old occaionaly used metal framed barn)
TLDR: If its got a trip rating in fraction o an amp (0.03A) or is to BS4293 (newer RCDs are to BSEN 61008) then its current operated and is just another name for an RCD, it its for additional protection then it nee to be 30mA (0.03A) {or lower - but thats rare}
The old VOLELCBs are to BS842 and are normally black bakalite looking things with a yellow trip butto, though ciltern did later make same white coloured ones. I've not seen a VOELCB intregrated into a consumer unit, they have always been separate units AFAIK
http://www.eec247.com/emergency/elcb_closeup.jpg
