The Intel 600p 512GB is faster than regular SATA600 SSDs, but overall the performance is a lot closer to SATA600 SSDs than PCI-Express SSDs. The only good factor about this product is the sequential read speed. Because it does not have the bottleneck of the SATA600-interface it performs a lot better. That said, the read speed drops a lot as the blocks become smaller: with our 64k and 4k test we see that the performance goes down quite a bit. The write speed is nothing to write home about either, especially compared with other PCI-Express SSDs.
The Intel 600p can definitely be interesting for some purposes. For example, it could be interesting for laptops, as an M.2-slot is the standard with smaller laptops. When expanding the storage of a laptop you can still choose SATA M.2s, that offer less performance at the same price as the 600p, and PCI-Express SSDs, that perform a lot better but are also more expensive. For this target audience there is a higher performance level at a lower price, which is always a good thing. If we can trust the specifications given by Intel, the power consumption of the drive is not that bad either. Bear in mind that you need to have an M.2-slot that support PCI-Express, because this is not always the case with laptops.
This makes the 600p fine as an alternative for SATA600 SSDs. However, as an alternative for faster PCI-Express SSDs it is definitely lacking, because the performance is a lot closer to that of SATA SSDs. The price reflects this: at the time of writing, the 600p is the cheapest PCI-Express SSD available. If it would have been released a few years ago, it would have an excellent price / performance ratio, but right now there are more interesting alternatives available that do not cost a lot more. For example, the 960 Evo costs about 11 cents per gigabyte more, but offers significantly better performance.