Piatnik have making playing cards since 1824, so they know what they're doing.
These cards are made specifically for playing poker - they are 88mm by 59mm, which speaks for itself. They are labelled with the standard English letters, numbers and symbols, making them easy for people to understand. The reverse side - the side you'll spend most time looking at in a game of poker - has a nice attractive design. The quality of the card and the finish means they slide easily over a card table, which is handy for both the deal and the fold.
Although these are essentially poker cards, they can also be used for most other card games, including whist and bridge. I don't know whether they would work for Blackjack (to be honest, I haven't tried), but I think that they probably would.