Fan convector vs traditional radiator

 Take a typical cheap radiator e.g. Milano Compact Type 11 1400x600mm (£104)

It has these specs:

BTU at Delta T30 2178

BTU at Delta T50 4208

BTU at Delta T65 5902

Watts at Delta T30 638

Watts at Delta T50 1233

Watts at Delta T65 1730

And stands 73/86mm off the wall

The same sized fan convector, the Milano Mono 1400x600mm (£409)

Has approximately double the heat output:

BTU at Delta T30 4203

BTU at Delta T50 8166

BTU at Delta T65 11475

Watts at Delta T30 1232

Watts at Delta T50 2392

Watts at Delta T65 3363

And stands 134/147mm off the wall

Other fan convectors I have found:

Smith Eco PowerRad 1500x400 1.5kW @ 50degΔC = 20% better, but slightly smaller

Myson iVector MK II iV60x160 BN 4.4-9.2kW @ 50degΔC = 4x better than standard radiator!

Mitsubishi iLife2 Slim 80 1537x579x131 2.4-4.2kW heating @45deg flow and 20deg room temp (is that a delta T of 24deg?  In that case the ratio is similar to the Myson)