The HDD portion runs at 5400rpm, so anything that runs off of it will be slow. Programs you run often will get cached in the SSD portion and start or load quicker. They used to make 2.5" drives with the HDD portion at 7200rpm and they were great, but they have since stopped producing them and all 2.5" SSHD's from Seagate are 5400rpm. I had one briefly and before they changed the name to firecuda and was very disappointed as I was replacing a standard 7200rpm drive...I ended up buying another 7200rpm drive to replace it, everything that runs off the HDD portion was too slow.
IMO, the 2.5" SSHD's are not worth the money, overall a standard 7200rpm drive is better. The 3.5" SSHD with the HDD part at 7200rpm are great and I can recommend them.
No compatibly issues, the interface is standardized. As for reliability, it is as reliable as any other drive. Mileage will vary.