This is a time when it might make sense to do one thing, but if you want to learn other similar riffs or make your own in the future, it would be beneficial to not have your middle finger stuck there. Why? Because there is a mechanic and finger rhythm to playing that sequence, and if given different notes or positions on the guitar for a similar lick, you will not be able to use your "held down" method. Also, If you skip learning that mechanic your fingers won't develop at the same rate, and, eventually, you will have to unlearn what you have learned (which takes extra time) and learn it the right way in order to play it at a high speed. And there is one more point, your brain will have to shift gears between playing the first part of that phrase (all fingers individually) and then switch to playing with the middle finger held down. At a high level, I suspect it will create extra hurdles for you. Good luck