I have two sets of sandals. A 6mm cherry with the invisible shoe lacing(on right in pic). The other set is a 4mm cherry with hemp laces(on left in pic). I use the 6mm for trail running only. I use the 4mm in a limited amount of stores. The IS lacing is easier to use on trails cause I can drench it after wards with water to clean, and they dry fast. The hemp gets really tight once it gets wet.

I also give myself a little extra soling in front of toes. This allows extra slippage room when I run down super steep trails. Though the cherry does have a anti slip texture so my skin does not move on cheery much.

Floppiness is not a problem. If it is that generally means lacing is too loose.

I've also tried the 6mm trail nubby vibram, but the tread makes it a bit too thick for me. Also the top of soling does not have the anti slip effect. Skin will move around more on that material.

My tie method really is as simple as it looks. Though lacing tightness is just as important as any other tie method.