They're not as messy, unattractive, hard to keep alive, or tasteless as the Cornish X too.
The issue though is that when you want decent meat or dual purpose birds, you're really not going to be very satisfied honestly with hatchery stock. I'd say you are relatively safe with Dorkings, but Hollands, La Fleche, and Crevecoeurs especially you'll get smaller and skinnier birds than the breed standard calls for.
Redcaps are so rare I don't know what you'll get though. Chanteclers may also vary per hatchery.
If you find yourself loving the idea or the actual act of raising up old-timey good tasting moderate to slow growing breeds though, the best route is to go with quality stock. Though it may surprise some - show bred lines are almost always bigger and meatier than hatchery stock. And in some breeds, traits like foraging and better feed conversion is improved in non-hatchery stock.
Nothing beats the "instant gratification" from Cornish X yes and nothing beats their breast meat, but not everyone loves purely breast meat, and not everyone wants a "freak" to raise up for dinner.
Plus, purebreds you can breed and hatch out your own from, not by new each year.