After you use them, they go back into your deck. When I draw it again do I play it immediately and draw another card, or does it take up one of the spaces in my hand?
If it's the latter they don't seem that useful.
[Edit: Oops. Mis-read "hand" as cards being available, and so considered the familair on the "table" as part of your hand. But as Ed says below].
Agree there is a downside when first drawn, but seems "useful" later as in a later hand one then might have your drawn hand cards plus the use of the bonus effect/s from the familiar. Might tip the balance for you.