It is reasonable - but for a horse not accustomed to the half halt the aids are excessive. You could hop on my horse after a warm up and try that and it would probably work. But before a warm up, or on a young horse you're going to end up with a tight, PO'd horse. Think about riding the horse, surrounded by a colander. Think of "closing" or "covering up" the holes as a step towards collection - where a grand prix horse rides around in a bubble where the horse is nearly 100% collected. When you first get on the horse, all the holes are open, when you start a young horse, all the holes are open. On an upper level horse, after an initial walk on a loose rein, we can fairly quickly start closing up holes. On a young or inexperienced horse, we have to take time to close the holes and if we can close up one or two in a ride - it was a good day.
Riding the half halt like this is quite constrictive in that both legs are driving (closing holes in the back of the colander), the outside hand is closing (closing holes in the front and side of the colander) and the inside hand is closing (closing more holes in the front of the colander). So we've taken the horse from no holes closed, to 8-15 out of 20 holes closed in the span of a stride. A young or not warmed up enough horse might either stop, rear, buck or bolt (mine would buck lol). So we must modify the half halt in the beginning.
For me, I start by riding the half halt with only the leg and the seat - asking for more energy with the leg and balancing the forward response with the seat while allowing the horse to stretch to the contact as much as he wishes (not letting the reins longer - just using the "give" in my soft elbow to take up the contact). The as I shorten the horse and close holes in the colander, I start giving half halts from the inside leg, a balancing seat and "catching" them with the outside rein (not constricting!). Then I can do couterflexed half halts with my outside leg and inside rein to increase suppleness. As my ride progresses I can eventually do the described half half, but never with a constricting hand! The fist may close, but the soft elbow must be ready to receive the energy from the hindlegs and allow the neck to fractionally lengthen.