Glad I stumbled upon this, two days ago I went to Stafford and returned today. I only booked it the night before, and was just fiddling around to try and get it cheaper. I often split at Birmingham with advances, and did this time, but took Chiltern from Maylebone. First experiences with them, and I was pleased. It was comfy, free wifi in standard, the tables were adequate. Yeah, you have to take the advertising with a pinch of salt, but it was fine. I was impressed at £18 single, departing Marylebone at 15:45, only booked the night before. I only had a 168, so didn't experience a 67, but I was happy.
Today, I returned from Stafford direct first class, and yes, I prefer Virgin first class every time. So no, if I'm in an emergency and a rush I'm gonna take virgin, ultimately it is quicker, but when I wanna save cash Chiltern is a very good option, and more than just a back up.
On a side note, I also found such small formations leaving London to be weird, coming from AC/DC commuter land. I know diesels generally come smaller than EMU's, but coming out of Central London, it seemed odd. The Chiltern route seemed really popular. The oddest thing, was seeing the Stratford train as a 172, the whole concourse cleared for it, surely that one is crying out for more capacity?