I've tried several haptic feedback devices, and hav just bought a secondhand HF8.
I already had an SRS simshaker 4, and also a Buttkicker 2 with a better amp, and I briefly tried a woojer haptic strap.
IMHO they're all a compromise, between convenience, comfort, immersion, and software cost (payware/freeware).
The Woojer was very poor (understandably), weak, uncomfortable to wear, and no sophisticated haptic feedback from sims.
The SRS simshaker 4 is the most sophisticated, with 4 genuine transducers and good software support in the SRS app which also runs my windkit and motion platform. The big drawback with it is the seat cushion, with the original very soft foam and the fairly large hard transducers, making it like sitting on a sack of spuds !
I improved things quite a bit by fitting them into a shaped memory foam cushion, and previously I'd even tried them within a foam seat base itself, carving out cylindrical pockets for them. That was excellent, but my latest seat, an elite ES1, has thin foam pads, so not possible in that. It's a very comfortable abs shaped bucket seat, so the SRS transducers (in any cushion) lift me up too high, reducing the comfort.
So I then tried a Buttkicker, underneath the seat, so no interferance with the seat shape. That gave a new problem though, because that was shaking the whole rig "err indoors" downstairs complained about the vibrations in the ceiling.
Hence now trying the HF8.
So far, so good. Simple to fit in the ES1 bucket seat, nice and thin, so not lifting me up or pushing me forward too much, and the combination of next level's own HF8 software for driving sims and simshaker for aviators for flight sims works quite well when you get it adjusted properly. Being "in" the seat (like the SRS) the vibrations can be felt more easily at lower intensity, so no complaints from the lady downstairs !