Well since all the physical drives are just mapped to one logical drive the data will get written to whatever location, and AFAIK Windows does not provide a way to allocate the specific destination block by physical drive to which it will go -- only to the logical drive when there are multiple physical drives in the logical drive. JBOD is really not an array in the sense of RAID, but rather just a concatenation of all of the physical drives into one logical drive. In other words without SRT the SSD will not perform caching for the HDD but would just be the first or last bunch of blocks where data is written.
How are you implementing the JBOD, through spanning into a volume set in Windows or with motherboard/add in card RAID? Although JBOD is not RAID many controllers allow it as an option, which is where I have concern that the SSD may lose TRIM support, that the controller would not pass the TRIM command until RST 11.5, although I am not sure that if that is an issue that 11.5 will address it, as it is directed at RAID 0. If you are implementing through Windows you may still have TRIM capability as there is no controller in the way, which seems to be the issue currently.
Another negative is that you will lose unknown data if a drive fails, maybe nothing significant, but it really depends what ends up on that drive.
While I do not recommend it, and I would prefer using the SSD alone for best performance, a more controlled approach would be to use Intel SRT for caching. Then at least you know you will get a performance improvement for the HDD.
The real useful purpose for JBOD for home users is to allow drives of different sizes to be combined into a larger volume, no performance advantage.