HW100's already had a known fault with cylinder threads on early models. As stated the repair to the gun didn't involve the air cylinder, however reading your highlighted post there is no mention of the part that failed being non standard?
I have no issues with non standard cylinders as long as they are from a proven source. As vice chair of my club the only time I would seek to have a member or visitor banned from bring a cylinder to the club would be when it has been unsafely modified or has a proven or obvious defect, for example people who have buddy bottles with quick fill adaptors drilled and tapped into the base or as I have seen an air arms s4** who's owner drilled the front stock for a sling swivel and who went through the thin wood and onto damage the cylinder. Each case must be weighed on it's own merits and a blanket ban is in my opinion a knee **** reaction.