The faster meter does take some getting used to. Getting them now will make you struggle now and you will not face the same when you make master. The faster meter's are very tough to master though. I cannot ever ding them consistently. And the more precise the irons the more unforgiving they are. Your good shots will be very good and your bad shots very bad. The raptures on the other hand are very forgiving and easy to play.
About one vs two upgrades -- You may have to upgrade again after making master as the master irons are very precise with more distance and help tremendously. Although some master's also play raptures.
If I were to go back, I would probably buy the faster meter precise pro set, and then again upgrade on becoming master.
Renting and trying the diff sets for a day each may help..