I really like this GHD because, if you train at home, you can divide it in two pieces and store it away easily. And it is also very useful for isolating the hamstrings and calves (there are videos on YouTube on how to correctly do the exercise), specially if your lower back is already fatigued from heavy compound lifts.
Is this exercise a must? Is this exercise the reason you don't squat 300 kg? I would say no. You still want to do barbell good mornings for squat hamstring strength, and heavy RDLs. However, this exercise is unique. Its totally different from a Nordic Ham curl, and it is a beast of a compensatory exercise for the knee, a lot better than classic machine/band ham curls. When you deadlift or squat, you activate the hamstring but you are extending the knee all the time. Well, for knee longevity you also want to do knee flexions (against resistance of course). And the GHD is perfect for this purpose, sice you do the knee flexions with high intensity (normal machine ham curls are ok but they are not as beast as GHD).
Now, as a sidenote, you still want to be careful with this exercise. You want to warm up your hamstrings, and control the exentric. Just after it arrived I tried it and I could already do GHD for 5-10 reps, but I know this is not the case for everybody. If you dont push your butt back and cheat, and you keep your butt extended, this exercise is brutal for developing hamsring strength and grinding capability (a lot of people push their but back shortening the ROM, this is the best way of making a beast of an exercise useless). I say you want to be careful, because I dont feel this exercise is made for loading it with weight vests etc, and it has a good excentric component (so control your reps). I find that after doing lots of eadlifts, my hamstrings feel tweaky if I try to do GHD as a finisher, so I prefer to do this after squats or medium weight deadlifts. If you feel tweaky in your hamstrings, call it a day. To make sure you avoid any problems, make sure you are hidrated and you take enough salt, specially if you like caffeine, which dehydrates; also, listen to your body!! If something feels tweaky, dont push it.
I bought it because I think that hamstrings are crucial for knee health and for strength in powerlifting. If you have the money and the space, definitely go for it, you won´t regret it. The price is also a steal, since normal GHDs are very big and pricey, and even a famous company (you know which) has the same 700 $ price tag for both their normal GHD and home GHD which doesn't make any sense to me (or to your wallet).
Have a good rest of your day!!!