There's a big difference in riding style and control between a regular 2 cylinder and 4 cylinder bikes.
2 cylinder bikes have a bigger torque range so it's easier to ride.
4 cylinders have a narrow torque range, if you rev and hit that sweet spot while cornering you're gonna skid.

It takes some skills to ride a 4 cylinder 'properly'.
ZX6R has a higher compression ratio and is also 4 cylinder btw.

2 cylinders like ER6N/F have plenty of useable low end torque while riding in cities and still capable on the highways.

For TS, you'll grow out of a quarter liter bike very quickly so I suggest saving up for an ER6.