they are open, but i barely use them, i prefer not to use trick decks, most of my spectators want to check the deck out, and they always look for markings.
First, stripper decks don't have markings. I let my spectators examine them all the time and no one's ever guessed there was anything special about them.
Second, with a little roughing spray, you can convert the Svengali deck into a Mirage deck. It gives you a lot more options, none of which have anything to do with unique marks on the card backs. And by itself, unaltered, the Svengali is an excellent forcing deck. There's no need to do the straight-up bit of "draw a card, it's now on top, now they're all your card".
Third, the marked deck is good quality for the price - that's doesn't mean it's the best marked deck ever. If you want top-notch, you can shell out for the new Maiden Back Gambler's Deck, or snap up the Ultimate Marked Deck before they disappear - I bought mine for around $30, and now that USPC has banned altered Rider Backs, these out-of-print decks are selling closer to $40 in some shops. That's like the Rolls Royce of marked decks, short of any that use juice, dabs, UV ink, etc.
