I used your calculator for a bedroom, it calculated the heat loss at 1065 Watts, which is about right, and says that with water type, the room needs 6.5metres of skirting heater, so buy 3 lengths at 2.5 metres. This exceeds the length of the room so it would go along the front wall and one other. It would have to be a wall without wardrobes or bedhead against it, and the room does not have thee unobstructed walls so it would only be possible by removing existing wardrobes.
With Electric type it would need one 2-metre length (400W) plus one 1-metre length (200W) plus one 400mm length (80W)
The cost of this per the website would be
water type
3 lengths at £148 each = £444 (don't know if this includes VAT as it is not mentioned) plus maybe some fittings and connectors, cost unknown.
electric type
2m element £65
1m element £45
400mm element £24
casing at £72 per length (not stated but I will guess 2.5m) x 2 = £144
temperature limiting device (this might be what in English we call a thermostat) £9.60
total £287.60
(don't know if this includes VAT as it is not mentioned) plus maybe some fittings and connectors, cost unknown.
Compare the cost of the water type at £444 with a steel convector radiator of 600x800mm, output 1111W at £48.99 inc VAT. I have omitted the cost of the valves since they are very unlikely to cost as much as the valves on the skirting system.
Compare the cost of the electric type at £287.60 with an electric convector at £19.99 which would be just as effective, or a low level electric heater at £ 60 that looks nicer. Either can be mounted on the wall.
You can of course buy more expensive panel heaters if you are anxious to spend more.
Personally if I was fiting a radiator I would fit a larger one at insignificant extra cost, since it would have the power to heat the room fast from cold, even in abnormally cold conditions when extra heat is required. This would cost quite a bit more with the skirting system since the parts are so expensive.