This looks quite good on paper cost/performance wise, but as I have already seen multiple times, it can be at the cost of proper cooling. Eq. there are many cheap and beefy laptop systems being sold that have brutal overheating issues once you actually try to make use of all that CPU/GPU power (I've seen quite a lot of people using special fan-equipped notebook stands to combat this). They could also be quite noisy & the overheating issues could reduce the overall lifetime of the laptop.

Depends on the type of the individual SSHD - if it does the chaching transparently (as noted earlier) or if it registers as 2 separate bloc devices (and OS does the HDD caching). BTW, some notebook have small MSATA SSDs that they use for HDD caching.