Kelvin
I had a Mackay 29 roller single axle cable operated override mechanical brakes trailer under a 5.6 m al boat up until I bought the Seafarer Vagabond that is on a tandem electric over hydraulic braked Mayfair Tinka (Redco comes from there too) The Tinka has 55 rollers according to a mate who counted them the other day.
Both excellent and are fit for purpose.
The owners of Mackay (ex dairy farmers way back,) are very helpful knowledgeable people and were good to deal with.
The Tinka has also been looked after by a gentleman who used to work for Mayfair.
I guess what you go for is subjec t to the boat your going to use it with.
My Tinka only gets the rear tyre and a little bit of the rim wet when the Vag goes on or off as I use a 912 winch with a pulley block. (double cable slow but with enough rollers its easy) No more brake or bearings or rotor issues and almost no maintenance is required.
If you get a 912 power winch (or similar) there are a few tricks you need to learn re successfully using it. Your boat, based on the pic would be good on lots of rollers with a power winch.
There are also a few tricks to getting the boat off and keeping things under control and your bearings brkes and rotors out of the salt.
Cannot comment on the Belco
Hope this is of some help. Ask if you want more info.
Cheers
Chimo