I presume that your mileage with this tool may vary. The quality of the tool is fine, however the design itself requires a wide spring pitch and may only be useful on very light duty springs (wide pitch or very narrow wire diameter).
I had hoped to use this on the heads of a Mitsubishi 3.0L V6, however there is simply not enough room to get the lower jaws low enough in the spring to compress it sufficiently. There were other space constraints around the spring as well on this particular head making it difficult to properly place the compressor (for some, not all, valves).
Before purchasing, take a good look at what you are working on. Make sure that you have room around the spring for the jaws of the tool and ensure that there is sufficient gap between the coils to place the tool. If you do not have the space, consider a different design.