I frequently see trainers touting the Vertimax as the solution to all vertical jump problems. There are two issues:
McClenton et al. (2008) compared depth-jump training to Vertimax training and found:
Depth jump training twice weekly for 6 weeks is more beneficial than VertiMax jump training for increasing vertical jump height. Strength professionals should focus on depth jump exercises in the short term over commercially available devices to improve vertical jump performance.
McClenton, L.S., Brown, L.E., Coburn, J.W., & Kersey, R.D. (2008). The effect of short-term VertiMax vs. depth jump training on vertical jump performance. Journal of Strength & Conditioning Research, 22 (2), 321-325.
Carlson et al. (2009) compared strength training, plyometric training, and jump training with a VertiMax and found:
The findings of this study demonstrate that there is no difference in vertical jump among strength training, plyometric training, and jump training over a 6-week timeframe.
Carlson, K., Magnusen, M. & Walters, P. (2009). Effect of Various Training Modalities on Vertical Jump. Research in Sports Medicine: An International Journal, 17 (2), 84-94.
One issue with the second study is the use of plyometrics, as that has become a colloquial term that has lost meaning (Flanagan & Comyns, 2008). Many plyometrics exercises use the slow stretch-shortening cycle (as would VertiMax) with ground contact time longer than 250 milliseconds and large angular displacements (Schmidtbleicher, 1994), whereas depth jumps utilize a fast stretch-shortening cycle with ground contacts between 100-250 ms and small angular displacements (Schmidtbleicher, 1994). The above results would suggest the need for fast SSC training to improve vertical-jump performance over a six-week training cycle.
This does not mean that the VertiMax is without use or a bad product. However, plyometric boxes are a much less expensive purchase that can elicit the same or improved benefits, at least over a six-week training program.
Secondly, and of primary importance, McGill et al. (2012) found that the broad jump predicted basketball performance measures better than the vertical jump in college basketball players:
Dependent variables of performance indicators (such as games and minutes played, points scored, assists, rebounds, steal, and blocks) and injury reports were tracked for the subsequent 2 years. Results showed that better performance was linked with having a stiffer torso, more mobile hips, weaker left grip strength, and a longer standing long jump, to name a few.
McGill, S.M., Andersen, J.T., & Horne, A.D. (2012). Predicting Performance and Injury Resilience From Movement Quality and Fitness Scores in a Basketball Team Over 2 Years. Journal of Strength & Conditioning Research, 26 (7), 1731–1739.
The implication of the second study is to suggest that vertical-jump performance is not of primary performance to basketball performance, and other qualities such as change-of-direction speed, balance, and acceleration likely have more to do with on-court performance.