Eliminating the drum is a major benefit in different ways:
Firstly: it is by far the most expensive part of a lotension spiral. It’s complicated to manufacture correctly.
Secondly: it needs regular maintenance/cleaning, especially when your working environment can get greasy (oil/frying) and disturbs the friction coefficient.
Thirdly: it uses up all the space in the centre of your line, which makes maintenance and cleaning difficult and time consuming.