I shoot with a group of 10 guys that have been shooting for a long time..they all use it and I can tell you its pretty much spot on. So much so that I eventually got the Istrelok for my ipad..yes its very accurate.
Howdy Tall, Basically and fundamentally, G1 ballistics are based on a projectile with a rounded ogive (point) and a flat base. G7 ballistics use a projectile with a modern boat tail, nosler type form. The latter is more aerodynamic obviously. Even though the G7 BCs seem 'lower' they really aren't when compared to other projectiles using G7. G1 and G7 are both 'valid' within their scope, but G7 is more accurate and uses a more scientific model. If you attempt to compare them, it's apple and oranges, both are fruit, round, and tasty, but come from completely different trees! There are several great threads and articles in this forum and make really interesting reading.
Hope this helped!