Pity I cannot fly that floatplane off to a good fishing spot as I need to do a BFR in a floatplane!
Design feature endorsements do not require a flight review (about the only thing that doesn't!)
61.385 does require you to comply with a general competency requirement for that particular aircraft type.
61.385 Limitations on exercise of privileges of pilot licences—general competency requirement
(1) The holder of a pilot licence is authorised to exercise the privileges of the licence in an aircraft only if the holder is competent in operating the aircraft to the standards mentioned in the Part 61 Manual of Standards for the class or type to which the aircraft belongs, including in all of the following areas:
(a) operating the aircraft’s navigation and operating systems;
(b) conducting all normal, abnormal and emergency flight procedures for the aircraft;
(c) applying operating limitations;
(d) weight and balance requirements;
(e) applying aircraft performance data, including take‑off and landing performance data, for the aircraft.