on thinwall tubes you need the tangent to the die (the bit that's being bent) to be fully supported around the circumference of the tube. otherwise it will wrinkle. Those plumbers benders won't do that. Look at how the cobra (and diacro) does it with the follow-bar.
The type of bender you need really depends on the radius and angle of bend.
Swarf uses a few machined blocks on bearings in a flypress. as do brompton. This is perfect for minor angle changes. brompton main tube, swarf seat-tubes etc.
If you have wrinkling issues you can also use cerabend (it's called something else in the states) which works like sand, it's a mixture of bismuth and lead, melt it in, let it freeze then melt it out once done. It works well and allowed us to bend tubes in some press-forms in a vice. BUT that shit is nasty. make sure you're properly masked up for using it. I've heard freezing water into a tube works too, but you will need a HEFTY bender to bend that.