Have shot a couple of Grn Mtn barrels in the past, but they were all pre-X (honed) barrels. While excellent, accurate barrels, it took several thousand rounds to get them properly 'broken in'. 
Just started shooting a new 40-65 Grn Mtn 'X' barrel on my CPA. While it 'seems' very accurate, I'm really just getting started on developing loads, but expect good things. However, I will remark that it as good as any Bartlein cut-rifled barrel I used as far as clean up and lack of leading. Shooting 20-1 cast bullets and 62gr of Swiss 2F it takes almost zero clean-up after a match or a day at the range. Next to casting, I like cleaning my rifle the least. But, this barrel takes about 5 minutes of cleaning before going into the safe. Props to Grn Mtn for an excellent barrel.

"Honed" barrels.   Extrude-honed, maybe?  Would seem a natural for that process.