Because it’s not advisable to use the filter with hot water. The materials in the replacement cartridge’s housing aren’t designed to withstand high temperatures and may melt. If you need hot water, switch the filter to unfiltered mode.
Yes, of course you can safely remove the filter from one tap and fit it to another one! The thread quality allows you to change tap repeatedly — when you move house, when you go on holiday, etc. You can take your TAPP Water filter with you when you travel and even use it in hotels!