Hello bobster.
Yes, both the Secur straps and Torse straps work perfectly well.
However, as TreeFlex rides low and I am tall, the Secur straps were at the end of their range of adjustment for me. This means that when I use them as shoulder straps without the Croll they are a little tight.
I am very happy with the Torse straps however. There is much room for adjustment, and they are quick release which makes them very nice to use or not use as the case may be.
Whichever you use, slip the webbing through the spreader buckle between the shoulder blades till the adjustment buckle sits just above the collar bone.
I hope that helps.