plastic tube??? plastics not known for its good thermal transfer qualities.. a SS coil would be best, its basically the same concept as a shelf chiller. with copper tube it would need less than 2m imho (based on herms coil length) but copper can react unfavourably with some beers.
Its an expensive way to chill as you need a few bags of ice to chill the coil and prime for each session, and dont forget to stir while you pour to avoid 'cold fingers' (honest thats the term for cooler water hugging a hex coil)
tho if not happy and bough online return it under distance selling rules,
a cheap n easy method of matting two tubes that wont be under huge pressure is a short length of silicone tube with a slightly smaller inside diameter
cable ties or jubilee clips can be used to strengthen the seal..
wrong time of year but an ebay bargain shelf chiller is a good deal, and you dont need to run for hours, i run one for 30-40 mins of an evening til it hits 0c to chill an evenings pourings for myself.. the waterbath retains the cool
the ice wall is only needed to keep up with rush hour demand in a busy bar... I keep meaning to mod it so i can power the recirc pump independently to avoid the cold fingres when the compressor is off.