With all due respect, without sharing NDA protected information about the specific quantity and model numbers of FS switches I have personal experience with in a certain network, there are very valid reasons to have significant concerns about the stability and feature set of the operating system that ships on them.
There is a reason they are abnormally cheap, in exactly the same way that FS transceivers which are literally the cheapest 1Gbps and 10Gbps OOK optics you can "Add to cart" and buy online are the cheapest transceivers you can buy on the market.
But by all means please go ahead and use FS switches for all the layer 2 aggregation needs in your network if you think that they meet your needs. I'm not stopping you.
If an ISP has a serious enough need for a large quantity of whitebox switches based on known switch-chip vendors' ASICs I would encourage them to send staff with experience in the electronics manufacturing industry to every year's Computex Taipei and speak with the manufacturers in person.