I needed to put together a couple of strut assemblies. I shopped around some as I really didn't want to spend a bunch of money on a tool that I would likely use only a couple times. Sure I could have rented, but I'm something of a procrastinator and a night owl, so owning it outright was just going to work better for me. There were plenty of styles to choose from, but most were simply too expensive for my purposes. I narrowed it down to this one and a similar unit that Harbor Freight was selling for about half the price. I chose this one because it appeared somewhat more substantial. When I finally got it and was able to examine it closely, however, it was apparent they were both pretty much the exact same thing.
As is the norm with Amazon, it arrived in an acceptable amount of time and in good condition with no defects and nothing missing. The unit is pretty much as it appears in the picture--two large clamps that go on opposite sides of the spring. Each clamp is effectively two large cast hooks spanned by a large bolt. Place the hooks at the top and bottom (well, one or more coils in actually--the top- and bottom-most coils need to engage the spring seats unobstructed) of the spring and tighten the clamps down equally. Included in the package, but not in the picture, is some additional hardware to secure the clamps to the spring.
The tool is a rather simple design, as described above, and works exactly as it's supposed to. The thing is, if you're using hand tools to tighten the clamps, you'll be at it for quite a while--and need a lot of elbow grease. Fortunately I had an electric impact wrench, which made things go far easier and quicker. The process is further complicated by the fact there's really no good way to hold the assembly securely; you want to leave the clamps free and the spring is large, round and not particularly substantial. Furthermore, the spring changes shape while being compressed, which not only makes it more difficult to hold, but also changes the geometry of the tool. I did get a little worried as the clamps angled outwards and tangentially, but the tool held firm and did the job without slipping or jumping. Careful positioning of the clamps is required to insure they won't get in the way during assembly, especially considering the spring's movement during compression. Upon releasing the clamps, it became apparent that something had shifted during the procedure, and thus a bit of pounding was required to remove the clamps.
Ultimately, the tool accomplished the job, though not without difficulty. Had I not had the electric impact, I would have had to spend all night on just one strut assembly. Also, it seems that this tool likely wouldn't work on springs that are currently installed on a vehicle, though that shouldn't matter with most strut arrangements.
While the tool does work as it's supposed to, it seems just a little more trouble than it's worth. I would recommend either purchasing or renting a spring compressor of a different design.