I have had one of the original DX6 since about 2005 or so,... Never had any issues.
As far as any 2.4 ghz radio, they all will have issues if the antenna is below the water line.
Water absorbs the radio signals at that frequency. Early on, fast boat modelers had issues with
just the rooster tails of the hydros and deep Vs creating interference. Getting your model down
in the trough, or behind a breaker could cause similar issues. Submariners still use 75mhz and 27mhz radios.(In North America)
Spektrum, Hi-Tec, Futaba, They are all good reliable radios.
Are there cheaper radios?, Yes, but do you want your model "offshore" when a cheaper radio fails?
The biggest issue I have found is there are never enough proportional controls.
And the 6-8 channel radios may be covered with switches and options, but those
don't always work best for a scale ship modeler that wants to run cranes, winches and
or even a thruster that simply needs a "three" position switch as opposed to "on/off".