I have been playing Diezel amps for about 10 years now. I have owned every model. I am not a metal player, but play many different styles, as needed.
ANY Diezel amp is easily capable of playing any style you can play. How you use the amp is totally dependant on your taste and styles of music preferred.
The higher wattage amps, the VH4 and Herbert, can be used in any venue from lower to higher volume settings and can provide any tone in your head. These amps come with midi switching as standard. These amps do work best at slightly higher volumes to get the tubes working a bit more, but are easily capable of being used in quieter venues as well.
The Einstein comes in two wattage variations, 50 and 100 watts, in a head format and 50 watts in a combo with reverb format. The versatility is definitely there in these amps, just as with the other, larger Diezels. What the Einstein does not have is midi switching built in. In my case this is no problem.
The Einstein, as with all Diezel amps, can be voiced to taste. By switching out different tube types, both pre and power as desired, you have the ability to really get the exact tones with all the nuances you desire from the amps.
The Schmidt is the baby Diezel with 30 watts, in a Class A format, with a terrific reverb voicing, and three channels. It has all the options of the other Diezels, but for midi switching. The versatility of this amp is as broad as anyone could ask for in all voicings (clean, mild chrunch and heavy saturation). Being a low wattage amp, it does not saturate to the extreme of the higher wattage Diezels, or get the low end thump of the VH4 or Herbert. But, it does anihilate any other amp in it's wattage class with ease.
All Diezel amps can take foot toys very well, and they all have versatile effects loops. The quality of every amp is identical in the care taken to build and insure each amp is working perfectly. The sounds available from every Diezel amp are easy to dial in fast, with lots of flexibility in each tone desired.
The quality is second to none and the amps, while each possessing their own feeling and tonal variation, bear the Diezel trademark for tone in varying degrees. All Diezel amps come with a compensated out feature. This is for using a guitar cable to connect with a P.A. instead of micing the amp up, if desired. I did a blind A/B comparison in a studio with a Neumann U-87 compared to the Diezel comp out. To be fair, I let the sound engineer set up the mic and choose between the two...comp out or live Neumann mic. The sound engineer could not tell the difference between the two. Another Diezel plus...no Diezel amp is ever started into manufacturing before Peter Diezel is absolutely and totally satisfied with the amp. I have owned amps by other manufacturers where they get an amp going, then sell it to excited buyers and make improvements all along the way for years. While Diezel amps are improved, they are only done sparingly, as the design and manufacture process is so thoroughly checked every bit along the way by Peter. Very little needs to be done, if at all.
The saturation is never harsh, or jagged sounding from any Diezel amp. The amps can all be dialed in to be as tame or viciously saturated as one desires, depending on the wattage requirements needed. Obviously a Diezel Schmidt at 30 watts is not going to have the same exact ferrocious attack as a higher wattage Diezel does, but it has an amazingly serious saturation that still remains clear and toneful, compared to other 30 watt amps by other manufacturers.
Compare any Diezel amp to other manufacturer's amps within the same approximate wattage range for tone, flexibility, build quality, and all other aspects, and you should find that there is no comparison.
If you cannot try a Diezel amp out prior to buying one, I never auditioned any Diezel amp out either prior to buying any of them. Not to worry. Consider the following for the closest match-up in an amp of your personal choosing.
How much wattage do you really need for most of your playing situations? Most of the time, in larger settings, P.A. personel will be micing you up anyway.
If you are miced up most of the time and play with a quieter stage level, I suggest an amp where the tubes can be run higher in dial setting to get the most out of the amp's tone...that is either a 50 watt Einstein or 30 watt Schmidt.
If you use midi switching for your effects consider the other, larger Diezels with midi swithcing capabilities, the VH4 or Herbert.
If you play heavier music styles consider the larger Diezels, such as the VH4, Herbert or 100 watt Einstein.
If stage space is a problem, consider a combo Einstein or Schmidt.
There are other obvious considerations to be made, but there are other posters here to offer their suggestions as well. No other amp that I have ever played through offered me all that Diezel amps do, no matter which amp, what style of music, which venue type, or band situation I have been in.
They are simply the best sounding, best built amps I have ever heard.
); well, when I first played a VH4 (note: the very first Diezel I played in my life) it took me just a few minutes to get a satisfying tone from all the 4 channels!!!! 
