OK, I read the article you mentioned...first let me say, I am not partial to either the Lee or FH systems, not endorsing them either way...this is just my opinions...
They are essentially the same system with different holders and potentially different filter materials. Lee uses glass, while it is fragile, it isn't as easily scratched. My LEE GND that I use all the time, will likely need to be replaced after my next trip, it is plastic, and scratches. I have never had issue with the Lee FIlter holder popping off, even when I carry the camera on a tripod with the filter ring and holder still on the camera, never with a filter in place...but still, that is hiking, walking, shaking it around, I have never had it fall off. If the guy who wrote that had it fall off when he tilted the camera down...it wasn't on right and it was operator error. The BS filter isn't a thick hunk of glass...its thin and light, certainly not heavy enough to pull the holder off the adapter ring. I actually quite like the ease of operation of the LEE Foundation system. Part of shooting LE is slowing your process down for many reasons. To want a system that is just faster...or to cite that as a pro over another system...seems pointless to me. LE is long, and slow..it just is. My two glass filters have no scratches, and they get used a lot, sometimes they get put back in my gab with no case while I am swapping to make sure I don't have too much or note enough density and don't want to miss the shot...it happens, but they have survived.
The FH system, yes, the filter is aluminum, but that means its also heavier. A good bit heavier than the LEE, so much so that I don't know if my 24-70L will stay zoomed out to 24mm if there is any tilt up on the camera. And mine is not one of the loose ones, its tight, but the FH holder is substantial, and that comes at the price of weight. The attachment of the holder to the adapter ring, to me, is not as secure, it has a set screw that screws down onto the adapter ring, which if over tightened could bend the ring, and if undertightened, well, that is the only thing holding it on...just a bit leery of it really. When I have used the FH filters, I put them in my LEE holder. My Prostop IRND filter set is the resin set, I have not used them much, mostly because I don't have proper cases for them yet and don't want them getting scratched up. The Firecrest filters are glass, so just like the LEE, they are breakable...FH also makes you stick the foam ring on the filters, which was a PITA, and as hard as I tried, they are not perfect, they work, and don't become visible, but it was a PITA, and paying that much for something, it should have been done at manufacturing.
That article also mentioned availability...yes, LEE went through a period of low supply and high demand...I paid over retail for my BS, but paid retail for all of the other parts, and it took me a while to assemble my kit...which was fine, it wasn't cheap and it allowed me to do it over time, not all at once. FH, well, they are not much better. The set I have, was a prize, for winning an image contest...but its not the set I won, because after nearly a year, they still could not supply the Firecrest 10,13,16 stop set I won...I still don't have it, and likely never will. They have had issues with suppliers for the holder and filters...so its not a fair statement to say that FH is readily accessible...they aren't.
Bottom line...if you can, try out something if a fellow shooter has it...see what you like, see what works for you and your workflow, and your budget. They are almost equal kits in my eye...with minor nuances...