This set will let you play the game from 1st level to 5th level. On the slow XP track that can take quite some time to play through. You will likely be able to pick up PFS mods, or other early level mods and supplement your playing with those mods. The set seems to come with everything needed to play the game - dice, tokens of some sort, flip mat and such. A buyer literally gets a game in a box at a reasonable price and for much less monetary commitment than going the core rulebook route and the additional things you would need to get started that way.
... which makes it just like roughly half of the other pay-to-preview product that has failed in the last 25 years.
I don't regard the Holmes-Moldvay-Mentzer sets as "pay to preview"; they were all fully playable games with character generation, lots of monsters & treasure, and 3 levels of play; potentially months of entertainment.
Holmes comes pretty close to being a pay-to-preview product. But even Holmes was supported with an entirely independent product line.
As Pathfinder aims at something more akin to a month per level model it is likely that once a week play will take five months to reach the final level in the game.
Maybe "length of preview" combined with full compatibility will do it. (Based on TSR's lack of success with similar products, though, I doubt it.)
The problem with the pay-to-preview model is three-fold:
(1) People who research your products will note that it's pay-to-preview and will generally prefer to buy the full version instead of the dead-end product designed to be stuck in a closet and never used again. (People don't buy demos.)
(2) People who don't research your products, buy the product you tell them to buy, and then discover that it's something designed to be completely replaced in X amount of time will generally (albeit not universally) be dissatisfied with being misled.
(3) If you're joining a group that's already playing, you will buy the rules that they're using -- not some other version of the rules.
If Paizo succeeds, it will be because the Beginner Box is treated like a full game and results in a significant number of players running full campaigns using the Beginner Box and not the PFRPG core rulebook.
Given that:
(a) It's called the "Beginner Box"; and
(b) The bulk of Paizo's existing business plan is aimed at play which extends beyond 5th level
I'm skeptical that this will prove true.
But, as I say, I would be happy to be surprised here.