I have short runnels in epoxy resin countertop, probably similar to the phenolic resin Paperstone. I love them! I don't find them difficult to keep clean--just wipe them out when I wipe down the counters. Resealing would be a small sacrifice for such convenience, IMO. The only downside--they are so convenient, I usually have a few rinsed and draining items sitting there, waiting to be put away.

If you are using a dark color, and have hard water, mineral deposits might be a problem. I would expect that with any dark material--a gentle scrubbing should remove those.

I don't find them hard to keep clean. At any given time, there are probably a few crumbs there, but it is not really a big deal.

The Richlite fabricator recommended against it b/c they would be hard to keep clean and there could also be issues with the sealant breaking down b/c of the extensive water contact.

If the fabricator, who presumably has an intimate knowledge of the product and how it performs over time, is recommending NOT to do it, IMO, you're crazy to go against his advice.

Runnels are cool but I would not risk them in what is a paper product.

I agree with Angie_DIY, mine don't get dirty, just crumbs here and there. Mine are cherry treated with pure tung oil. If they fill with water after a lengthy dish washing session, I take the corner of a kitchen towel and run it down each runnel into the sink. Any crumbs go with it. No big deal. You can also use a hand vac to get any crumbs out. But honestly crumbs are rare, we don't prep near them usually.