Most tide clocks are decorative. They assume a lunar day of exactly 24 hours and 50 minutes, run at that rate forever, and drift out of usefulness within a fortnight in most places. If you want an object on a wall, that is fine. If you want to know when the water will be where, it is not.
The one specification that matters
Whether the clock can be set to a local tidal constant.
A tide clock without one is running an average that belongs to nowhere in particular. With one, it is running your harbour’s actual interval, and in a semi-diurnal location it will stay useful for months at a time.
Everything else, the case, the dial, whether the hand sweeps or ticks, is preference.
Where they stop working
Anywhere the tide is diurnal or mixed. A single-hand tide clock encodes an assumption of two roughly equal tides a day, and where that assumption fails no amount of calibration rescues it. Check what your location actually does before buying anything.
What to buy
A clock with a settable constant, a dial you can read across a room, and a movement you can replace. That is the whole list. Prices above about the middle of the range buy casework, not accuracy.
If you are choosing between two that both meet the specification, buy the one with the clearer dial. You will read it at a glance in poor light more often than you will study it.