I have had my Magnaflow with those cheap clamps you talk about for about two years now. They have seen two winters, mud, and rain. It doesn't leak(carbon deposits) or shows no sign of rusting. (Minnesota salted roads) Cheap? Yes, but does it work? Yes. If you don't want the cheap clamp style, either weld it together or pay a higher price for the better clamps. But just letting you know from my own experience. Good luck.
Two years might be ok, I just prefer the better quality stainless, wider band clamps as I plan to keep the vehicles a good long while.
If you still have the truck 5 or 7 years from now I wonder if you'll still have those original U-shaped clamps on there. If you need to tighten one up one day you might be in for a surprise when one either snaps or strips the nut. I've been there before with my Flowmaster system on the Vette and that car never sees salt or snow. The Vette goes in the garage in the fall and doesn't come out until we've had at least two or three good, hard rains after the winter salting season is finished.
Interesting you mentioned about rust. How's your Magnaflow system holding up? I was under the truck last weekend and my stainless Magnaflow system is covered in surface rust after 1 year. I'm a little suspect about the quality of the Magnaflow system after seeing that. It hasn't seen much winter salt, I've only driven it about 2000 miles over the last year, and only once through the salting period. It's mostly seen rain in the summer months. I had Corsa on my 93 STS and it never developed surface rust and that car saw a lot of snow and salt.
I used to love working on my cars when I lived on the west coast, not so much here as I'm dealing with so many rusted pieces on the suspension. I've had to cut off several things on 5 cars over the last few years, a first for me. My next used vehicle purchase I think I'm going to time with a vacation back home in AZ and buy a vehicle to drive back here. Then I can have a 5-7 year old vehicle that hasn't seen salt and I won't start out my ownership period having a substantial amount of rust on the frame/suspension.