I'd agree with stranding the Quartet and maybe the Equa on a desert island. The Vortex and the Enigma don't deserve that fate. They're well behaved puzzles once you get to know them.
Peter
GunmetalUnopened Aqua,TurquoiseOpened Blue, Green, Bronze, Silver, Gold, Purple Opened Black V1 + V2, Orange, Red, Titanium, Lime Opened HandMade Prototypes too scary to reassemble Gold CE set in Clear Sleeves
Haven't heard much about the Delta in this thread. There have been some reviews about it elsewhere.
It's obviously not one of the difficult ones, but it isnt a gimme either. It is one of the ones I like due to the way it feels in the hand and the way the pieces interact with themselves.
All I'm willing to say here is that that are several approaches to solving this puzzle. I've heard that force is needed, but I can tell you that there are ways to open it without any force.
This is one of those puzzles you can give to a friend and they'll struggle with it and then return it saying its impossible. It can be opened so quickly that you can open it in front of them and they still won't know how to do it.
Oh yeah, it can be open single handed, and blindfolded without force too.
Peter
GunmetalUnopened Aqua,TurquoiseOpened Blue, Green, Bronze, Silver, Gold, Purple Opened Black V1 + V2, Orange, Red, Titanium, Lime Opened HandMade Prototypes too scary to reassemble Gold CE set in Clear Sleeves
As far as I'm aware (and please correct me if I'm wrong), I don't believe any of the Cast series require excessive force to open. Several do have 'forced' solutions, but these are usually as well as a proper (more elegant) solution.
BluOb: Open (30/10/10) GrOb: Open (01/11/10) BlOb: Open (04/11/10) ROb: ... BluEx: Open (27/01/11) BrEx: Open (09/02/11) REx: Open (17/04/11) OrEx: Open (20/07/12) CuEx: In progress
Revo Mini: Open (05/07/13)