A few years ago, on delivery from Ct to Maine, DF wasn't working so bought
Hummingbird DF for $100. (now about $90.)
Made a captive reservoir and epoxed in.
Might not be my 1st choice but good unit for $.
Can't speak to other current unit as on my boat I am still using old Data Marine/DMI DF
that I siliconed in hull and has worked flawlessly for about 20 years.
Both install methods work, trick is to have no air/voids and make sure unit does not move
while drying.