the old style bolt has a female allen [hex] head; sized at 10mm.

the new style bolt is a 14mm shouldered cap head bolt.

I don't mind [too much] in-hex bolts for use where the tightening is light or moderate. There are times and places when using an in-hex head bolt, or an inside torx head bolt, is the only way to be able to have the fastener there and be accessible.

BUT, for a headbolt, in-hex is what I consider REALLY STUPID engineering.

...when I want to get a grip on a bolt and give it a good twist, or when I HAVE to give it a good twist, then I WANT to use a six-point flank drive socket on that bolt.

In-hex, or inside torx, are both inferior methods of applying torque to a bolt. ESPECIALLY when it comes time to loosen the thing.

Tightening a headbolt is one thing. Loosening it after a lot of miles [or TRYING to loosen it after a lot of miles] is something that can be altogether different.