If you have an intention of becoming Platinum elite at 75K miles, then go for it. If not at that level, run.

One pass is terribble at running a loyalty marketing program, not truly respecting it's elite flyers or their opinions. At the top tier, you get enough perks for it to be worth it. At the other levels, you would be subject to CO's ever changing benefits and issues.

as a 30 or 40 k a year flyer, you'd be better off with a reputable program on another airline. Then, if you achieve elite on UA or AA, CO will probably send you a free, unsolicited Platinume elite membership anyway.