The chinese cluster gauges, when they first appeared, were unreliable, and when one went bad, had to replace the whole unit. Some dealers had a "special" clause in warrantee for cluster gauges /forums/images/graemlins/crazy.gif They have improved to where they are generally more reliable than the individual gauges. The cluster gauges look better, have less wiring mess, and less install errors.
The individual gauges still have the ease of converting to other brand gauges. Many people replace the water temp and oil pressure with mechanical types. Maybe they have improved as well, but the older ones did have fogging, and were tempermental at times (fuel gauge). The older individual gauges were metric and the water temp sweeped to the left as engine got warmer. Not a problem, just weird. The individual gauges probably have more sweep, but doesn't mean they produce a more accurate reading. /forums/images/graemlins/wink.gif Converting the tach, is probably somewhat of challenge, finding one that works off same type sensor. ie no coil on diesel to use one of the low cost electrical tachs.