towbar wiring - skoda specific or bypass relay

 I am looking at getting a twobar fitted to my 2010 Fabia estate and I've been offered the option of vehicle specific wiring £100 extra 

https://www.pfjones.co.uk/skoda-fabia-all-models-13-pin-dedicated-wiring-kit-may-2010-292205.html

 or cheaper electrical wiring using a bypass relay

 i'm might very occasionally use it for towing a sailing dinghy but will almost exclusively be using it with a towbar mounted bike rack, rather than for towing.

http://www.northwesttowbars.co.uk/cykell-t31

 I can't particularly see any advantages of this more expensive wiring option for my purposes but would be happy to hear any advice on pro/cons

Thanks

Ewan