I think the best bender there is this one:
http://www.aircraftspruce.com/catalo...ges/464-fh.php
Mostly those benders are for bending soft materials like copper. The first Harbour freight looks sturdy, but I don't see how it really works. Any decent bender has a following die that is co-axial with the die one is forming the tubing over.
The second harbour freight bender is a cheap version of the Ridgid model, and the Ridgid is strong enough to bend rack tubing, but no longer made.
The die cast aluminum bender from AS is probably not going to hold up long bending 4130. They sell 4130, so you could at least ask. Presumably there is a reason they are selling the heavier version also.
I adapted a Princess auto bender and am very happy with it, but one needs a lathe, and the bender was medium expensive so most people would probably choose a different route. I started with something similar to this one, and all you do is alter the dies so that the round dies have a groove in them the size of the tubing you want to bend. I actually used weldable sprocket hubs for the die stock, and left the rollers intact.
This one looks like it might be tough enough, all steel, coaxial, and long handles as though they expect you to use some force with it:
http://www.harborfreight.com/cpi/cta...emnumber=98612
The radius of the bend still needs to be correct for your intended use, with the style I made one can vary the radius quite a bit.
In my experience propane is not better than mapp. MAPP is hotter, and that is critical. The main problem with either is the heat transfer is too slow. Either flame is hot enough to melt the braze, but the heat transfer is too slow for it to work properly. The flux tends to char up, and the tubing tends to get red hot because one needs that kind of heat to make the brazing work. It is odd because red hot is nearly 1500F, while the silver has a melting point considerably lower, but the propane or MAPP just can't get the heat up enough to really work it. You will notice the hotter the flame and the smaller the parts the better it works. With 4130, the red heat is not a problem, it isn't supposed to be done that way, but it won't harm anything. With AO at about 3x the temp the main issue is not melting the tubing. Even so, big enough parts require pre-heating. With a much hotter flame you can kick the temp up in a smaller area, before it has a time to conduct all over the place.
I wouldn't use AO in a home shop. It is a very odd animal, a fundamentally unstable gas at the storage pressures unless it is handled properly. I am using PO, but since I don't have AO, I don't know what I am missing.