Kelloggs discount at halfords

Looking at getting either a Giant CRS 4.0, Carrera Subway 1 or as a
treat a Boardman performance hybrid.

I got the voucher off the Coco pops, which doesn't say it excludes the
Boardman bikes.

Anyone used this for a discount?

I can also buy the halfords vouchers @ 15% discount so the bikes work

1. Giant via Winstanley £160
2. Subway £153
3. Boardman £305

Plus any advise on the above would be good.