I had put about 8k into my car and I didn't have the funds for the SZ set. There is a very sig price difference. They've been on my car for about 3 years and appear to be holding up well. No fitment issues and they still look great; no corrosion, rust or rot. I just picked up my SZ cat back (can't wait to get it mounted) but I have no reason to replace the Alloy' Toyz DPs just yet.
There are some knock-off items I wouldn't even think about putting on my car but if$$$$ is tight... having lower quality welds on some exhaust parts is unlikely to make a difference. And keep in mind if something like that does break it is not going to result in a toasted engine or anything dramatic