Router bits for FZ 10 box joint template

[Dongar]

I need to buy a bit to use for making box joints and am having trouble deciding between the 490 978 carbide spiral for $63.50 and the 491 079 Duroform for $120.00. Since the Duroform bit's cutter has two usable edges and the cutters supposedly last longer because they aren't brazed the cost works out cheaper the first time you have to replace the spiral bit. The spiral bit can't be resharpened for this use because the diameter would change and the box joints would not fit properly. I am leaning towards the duraform if the quality of cut is high enough. If anyone has ever use one for this or used one for anything I would appreciate your views on the suitability and quality of cut. Thanks Donald