need some help here guys

which one do i buy.......both have induction motor......the 3.550 is the newer model but dont like the thort of buying new detergent bottle everytime there empty or attaching the front detergent control to it (not pictured) the 3.65 has built in detergent tank but is the oldest of the 2 with a 1700 watt induction motor compared to the other which has 1800 watt

Your opinions.......please? Karcher K 3.550 Refurbished Pressure Washer :: Karcher Outlet

Karcher K 3.65M Refurbished Pressure Washer :: Karcher Outlet

i prefer the 3.65 as the detergent bottle is fixed on 3.550 it costs £9.00 for 1 litre (and i bet that dont work all that good)