Hi,
in comparison to trees that are made entirely of wire the sea moss will obviously not be as resilient to bending and crushing damage. However, the sea moss, after PVA and wood filler have been applied it adds quite some stability to the twig. The twigs are also quite flexible and do not break easily. The foliage nets hold the tree together and add further stability. I didn't try, but I'd say if the birch would fall on the carpet or even tiled floor it would much rather bounce of than break. With a wire tree the impact would deform the wire.
It also helps if you pin the bottom section, where you'll end up taking up the tree all the time.
I'd say it holds up well for gaming, but it might be a good idea to pad your storage container with some foam and I would not staple them on top of each other. It depends a bit how careful one is in general with miniatures. If you consider them to be playing pieces to be carried loose in a bag I would not recommend this kind of tree. If you paint them to a high standard and have a carry case add a slot for the trees and you are good to go.