Flexible tap connectors are not always simple to connect to pipes, as they often come with a ½ BSP male or female threaded end, people often connect these directly to a 15mm compression fitting or a 15mm isolation valve, but now there are much better options, such as flexible tap tail connectors or flat-faced isolation valves. This video shows how to use flexi tap tail connectors or flat-faced isolation valves.

You can see some videos where I have recently used flexi tap tail adaptors and flat-faced isolation valves here-
https://www.youtube.com/watch?v=UzjS2QpUMBw
https://www.youtube.com/watch?v=N-MyYzYwEhc

Links to the products are here-

Flat faced isolation valves on BES- https://www.bes.co.uk/flat-faced-straight-isolation-valve-15mm-x-1-2-bsp-pm-23573
Amazon- https://fave.co/2UV1NZj
Ebay- https://fave.co/2Ng9k3I