I received a TC Electronics BH550 yesterday and spent a few hours last night checking it out. I have a GK MB500 and was comparing the two side by side through the same identical cabinets (GK NEO 2x12).
Both amps are comparable in volume to my ears. The Bh550 can get really loud. I have no resources to bench test it.
The BH550 seems to have a lot more going on with the bass knob compared to the GK MB500. When you turn up the bass knob on the TC, you can really hear and feel the difference. The same goes for the Low Mid knob on the TC. The Treble knob doesn't create the super extended high end that the GK can produce but that's fine with me. I never turn the GK Treble knob past 1 o'clock anyway. It seems like the TC controls have a fairly flat frequency response in the 12 o'clock position compared to the GK.
I downloaded the Tone Print App and sent a Chorus effect to Tone Print #1 and Octaver efffect to Tone Print #2.
There are a lot of different Chorus Tone Print effects you can download but I just went for the 'classic chorus'. Sounds just like the description in the effect's title, a classic bass chorus with no low end loss. Homerun.
The same goes for the Octaver. Mutiple different type of octave effects are available. I went for the 'Smooth Octaver'. It gives an octave down effect and sounds like my Boss OC-2. But it tracks notes impeccably and could handle the low D on my bass with no problem. Another Homerun.
The built in tuner works. Unfortunately in two of the bands I play in I tune the E string to D in one band , and C# in another band. So I will still be using my pedal tuner. The Tuner appears to only do standard tuning. Too bad it's not a chromatic tuner ( hint to TC )
Only negative comment so far is I wish it had two speakon outputs. It only has one so you must daisy-chain two cabinets together. Not a problem as long as your cabinets are equiped with two speakon connections.
I will be playing a gig tonight, anxious to see how the BH550 performs in a live stuation.
here is a poor iphone pic