As bathroom spaces become more elaborate and mood orientated, consumers are looking for products that can emphasise these characteristics. "Designer" Radiators have turned what was essentially a utilitarian product into a design feature for any room. The fact that these items are now functional as well as aesthetically pleasing has led to a big increase in demand.
This has been the biggest single improvement in the area of "designer" radiators. Whereas before they may have been treated solely as "eye candy", manufacturers have realised that bathrooms also require practicality. Many of the newest designs are now capable of providing sufficient heat for a variety of bathroom sizes without the need for a backup heater. It is worth noting however, that the heating requirements of a particular room are dependent on a number of factors. These range from room height/how many outside walls/number of windows etc, so it is a worthwhile exercise to calculate the heating requirements of a room before deciding which "designer" radiator to have in your bathroom.
Top Tip - it is always better to overestimate your needs than underestimate. You can lower a radiator's maximum heat output but you can't force it to generate more heat than it's physically capable of!