A nail drill is certainly not a 'must' by any means. If it were I wouldn't have been doing nails by hand for 25 years.
You can go two ways:
1. Do perfect nails with your brush and spend very little time finishing by hand or,
2. Do imperfect nails with your brush and spend more time filing with an efile.
It is completely misguiding to say a drill is a must have item, that is just one person's opinion not a fact. It all depends on whether you employ good effective techniques by hand and how you work. The better you work with your brush, the less you have to file ... end of story.
I can easily clip off excess length faster than drill it down and with allot less mess ... I personally would never use a drill to shorten the length. Who needs the dust? Who needs the mess? I do not make thick enhancements so I do not need to spend any time to de-bulk that which is not bulky in the first place.
There is always more than one way of doing things. The skilful way using effective techniques and talent or the less skilled way and use a drill to correct the over use of product or a less than skilful application. Both work for the end result, but one will break down faster than the other .. I'll leave you to guess which one.