The Amici degli Uffizi card only makes economic sense if you are going to be in Florence for an extended period of time and are intending on visiting the museums it covers more than once. It used to cover a lot more of them than it does now (we bought family pass for the 2 of us some years back.) That said, maybe you don't mind not breaking even on it to have the convenience. Info on the website is current. Yes, you can enter the Uffizi without reservation with this membership: 4 members admitted every 15 minutes.
http://www.amicidegliuffizi.it/diventa_socio.php?pg=8&ln=en
http://www.amicidegliuffizi.it/home.php?pg=1&ln=en
Otherwise, only the most-visited attractions in Florence require or benefit from advance reservations. You are only allowed priority entrance with the Firenzecard for the Uffizi, Accademia and Brancacci Chapel with advance timed-entry reservations. See the card's FAQ section.
https://www.firenzecard.it/en/faq
Can't help you with making reservations with that card as we've never used it. Hope this helps!
(edited some typos)