I've used a few different types of hackamore but that's not one I'm familiar with. Seen them in photos but never in action.
I'm interested why you're thinking of trying a mechanical hackamore if your horse goes nicely in a sidepull. They have very different actions. A mechanical hackamore is much stronger for starters, plus it has the nose pressure and curb action that a sidepull doesn't have, and steering works differenty too. With a sidepull you open the inside rein in the direction you want to turn, so pull right to turn right and left to turn left (hence the name side-pull) whereas with a hackamore you are turning them from the outside rein, so push from the left to turn right and push from the right to turn left.
The nose pressure of a mechanical hackamore may come as a surprise to your mare if she's used to a sidepull bridle (and riding with the reins on a halter is essentially the same thing) so be prepared that she may not like it! You will also need to get used to carrying your hands higher and further forwards and learn to release the pressure on her nose as soon as you get the response you want.
As an aside I'm not sure what you mean by your new stable being "a little more spunky"? - or why that has made you want to try a different style of bridle.
Edited to add something a little more constructive!
My mare is ridden in a bitless bridle and like yours is used to a sidepull action. She is in a type of bridle called a "scawbrig". It's essentially a type of sidepull and works that way in terms of steering, but with the addition of a little bit of nose and jaw pressure when you apply pressure on the reins - for this reason it is sometimes referred to as a "natural hackamore" as it works on the same principle pressure-wise but is significantly milder due to the lack of curb action. That may be another option for you as it's a kind of cross between the two styles.
