You don't need anything new for the 17th that all the 16th edition testers dont already have.
The 2I RCD test is a load of BS spread by one of the lesser east european manufacturers that have it in their multifunction tester - there was an article in the NICEIC rag all about it. So don't get conned into buying a new tester when you don't need one.
One company even runs ads saying "The UK 1st 17th Edition Tester" which is strange since all the pre-existing 16th edition testers that have been around for years comply to the 17th edition.
Best testers I have come accross are the Meggers. Cant blow them up even accross phases, good readings, easy to use, 3 year warranty and made in good ole blighty - not some cheap imported tosh. I got a spanky MFT1553 in my hallway now and its the best.
Check out the promo video
YouTube - Megger MFT1553 Multifunction Tester