For honing razors, one Coticule of about 4cm X 15 cm suffices. Currently costs 42 EUR at Ardennes' Coticule storefront.
An irregularly shaped "bout" of size "7", can be had for 30 EUR. If you make sure to purchase one with at least one long edge of 15cm and the smallest end not less than 3 cm, that one too will do the job just fine.
The BBW can hone a razor as well, but it is not as fast and therefor less versatile. A Coticule can really start out on pretty dull edges, while a BBW may require some prior work on a coarser hone. For finishing the edge, Coticules have been used for ages. On the Belgian Blue, we're only at the first steps of finding out how to optimize the final results of that whetstone, trying to reach results that have a right on their own, without the need for additional work on other hones or pasted strops. The last few weeks I've shaved several times off a BBW with very good results. But more tests need to be done.
I think that eventually Coticule and a BBW compare like a horse and a donkey. Both will get you to Paris. But you might prefer to horse if you can afford it. Yet you might sympathize with the donkey
Best regards & Welcome to Coticule.be