Okay... Where do I start...
I'm warning you, this may sound pretty negative, but I spent hours a day at gym training giants on strap bar in level 5 with no spot, so I have my reasons.
#1- Strap bar, as I know personally, does not help at all in giants. You do not need to tap at all on strap bar to make it around, while on the real bar you need to severely tap to get a good giant. Also, shifting is a major issue. You do not need to shift on strap bar either, but you need to on the real bar. I didn't know this, so in my first attempt at giants I nearly collapsed onto the bar from lack of shift.
#2- You cannot train much on strap bar. Honestly, aside from training clear hips and giants, what else can you do than connect in or do many in a row? And when you do practice it, it takes multiple times to get it right, when you will still have to spend many more hours getting used to the normal bar when you get back onto it.
#3- Strap bar is dangerous. Many times, I would hit handstand, and then I would collapse onto my head, shins, chest, and hurt myself. And it is not just because on poor giants. Giants are my best bar skill now. Also, I've seen so many gymnasts on my team hit handstand, then instinctively try to twist off, and hurt their shoulder or fall sideways and seriously mess up their arm or shoulder in the process. And in the long term, I've bled from the use of strap bar. And that is when I was using wrist bands, the big fluffy kinds. Do they protect you? Yeah right.
These are my reasons, and honestly, after level 6, it is COMPLETELY unneccesary to use strap bar at all.
-GCG