RE: guillows have poor quality balsa?
Simple - Poor quality wood is of poor quality, and good quality wood is of good quality.
Sorry, couldn't resist.
But frankly, Guillows kits are a remnant from the past. I have been in this hobby literally all of my life (Going on 50 years) and I have never seen a guillows plane fly. In fact, I only know one person who had the patience to ever finish one, and he has several hanging from his ceiling, but they don't fly. I'd be afraid to put an engine in one for fear that it would shake the plane to pieces.
Is this something you're building, or something you're thinking of buying?
If you're looking for an RC plane, I would strongly guide you away from Guillows.