This has been discussed here before, so you might want to do a search.
Here's a good resource for one type of CSST "Wardflex".
http://www.wardflex.com/images/design_install_guide.pdf
If you were going to install their product, it would have to be installed according to those guidelines. Every manufacturer has their own guide, so if you're using Tracpipe, you need to go with their guide, etc.
Most people, IMHO, that are buying CSST at the Home Depot, don't have a clue on how to install it properly or what the requirements are. Because of this, and because of issues with the product itself (mostly related to the very thin wall), CSST can be a hazard.
What I've seen in the last 12 years is that initially there was a big move towards CSST in new home construction during the housing boom when home builders were really trying to figure out new ways to cut labor and cost from new home construction. THEN, there were a number of house fires associated with lightning strikes on the structure, where CSST became energized by lightning and the thin stainless melted causing catastrophic gas leaks and fires.
The CSST manufacturers responded to these issues by changing the installation requirements to include electrical bonding. The bonding requirements add a lot of complexity to the proper installation of CSST, and in many cases are ignored by DIYers to their own (and their families own) peril.
After the issues came to light, some jurisdictions came out with new, more stringent, installation requirements for CSST themselves, that tended to make CSST harder and more expensive to install. For example, they might require 1-foot of separation between the CSST and any adjacent conductor. This caused a lot of home builders to revert back to black iron pipe. It may be also that the housing slowdown made it easier to find trained plumbers so that a "quick and dirty" gas line solution was no longer necessary? That's a complete guess. But I did notice an extreme drop of in CSST being used in new construction around here.
Also...I'm not PERSONALLY 100% convinced that the bonding requirements actually completely fix the problems. I have no data one way or the other. I just know that black pipe has been used to successfully plumb gas for about 100 years and CSST hasn't. Further, CSST as originally conceived and installed, was not 100% safe even though the manufacturers successfully marketed it to many people. Now they sort of say "we had some problems, but as long as you install it properly, it's safe".
A. I'm not sure I believe them.
B. I know a lot of DIYers and many professionals don't follow all the guidelines properly, and history has shown that if not bonded properly CSST can contribute to structure fires if energized by lightning.
C. It's a violation of the national fuel code to install CSST if you are not properly trained and certified...meaning even if you install everything properly...if you aren't certified to the manufacturer's guidelines, your installation does not meet code...because you're in violation of the certification requirements.
That's just my take on it. YMMV.
Phil