Here is an old Six-10 sample I hit repeatedly with an X-acto knife til the blade broke. It's like a very hard plastic.
The filled hole is about 3/8" and the glue didn't sag out of the hole. I've also made some beautiful fillets but have only used it for repairs and not a lot of actual building so far.

I got mine at Johnstown Dist. also but there was another thread a while ago with other sources.