I’d just get a cell phone signal booster. I’ve found that a WiFi extender is good if you’re in a marina but if your traveling, our cell phone is our data connect by using it as a hot spot. The Digital Yacht system looks pretty slick but you need another SIM card and data plan from either AT&T or T-Mobile according to their literature..
You might find this thread a worthwhile read, if you haven't already seen it:
https://www.trawlerforum.com/forums/s30/reliable-wifi-boat-51771.html
The biggest problem I have found with connectivity on a boat is acces points have terrible bandwidth.
Even my cel phone in many "right on the coast" places has slow internet.
So amplification is still at the mercy of whatever access point you are connecting to.
An external antenna will help occasionally as you are distant from an access point, but then ....how much bandwidth is really there? Most marinas stink and coastal towns seem to be stretched thin.
None of the above is very techie as I am not..but just what I have found with different kinds of equipment while cruising the ACIW.