I did have a BT dect phone but the only problem (major show stopper
) was if you unplugged the phone line it wiped the saved contacts list... never buying BT one again
I have a Gigaset Go850 which covers both line line and Voip connections, oh and you don't lose all the contacts you slaved away putting in
The only honest observation about Gigaset is the rechargeable battery life seems very short before memory effect kicks in i.e. not holding charge, current lot bought in July 2019.
I do have a Panasonic dect phone and still has the original Panasonic batteries in it!
I'm now hunting for Genuine
Japanese Panasonic rechargable one's to swap out for these cheap eastern makes
Max 6 phones per base, but I think you can have more than one base so more handsets.