A "Compatible" balaclava works well under most ski helmets without major issues, but it isn't specifically engineered for that purpose like an "Optimized Helmet Fit" design would be. You might notice minor bulk or need to adjust it occasionally during the day, but for most recreational skiers, it gets the job done just fine.
This option is ideal if you're a general resort skier who wears a helmet but doesn't need race-day precision. The balaclava will sit comfortably under your helmet for typical ski days, even if it lacks features like flat seams or a helmet-specific cut.
The main thing to watch for is pressure points — try the balaclava with your specific helmet before a trip. If you feel any discomfort around the forehead or temples after wearing it for a few minutes, you may want to upgrade to an optimized design.