Single rail -- that's good. The 28amps for 12v power will give you 336 watts. Its been recommended to hold in reserve 20% of that power.
Based on your selection of RGB nodes you might get better or worse numbers, but assuming pixel strings (.356 watts/pixel), I would not run more than 750 pixels (nodes).
Its not a bad price, nor a bad unit. Just understand how you plan to use it and how you might be limited.
