IMO the VS Bassamp has one main flaw :
The tone pots (Bass-Middle-Treble-Presence).
They are graduated from -5 to +5 but they are not very effective between -4 and +4

.
The mid tone control is quite poor, and when you play bass, you want to be able to set your tone signature there. It is more a "low treble", not very pleasing to hear

.
The Bass control is only effective on very, very low frequencies (30 to 100 hz ?). In order to write this review, I played it on a GK 12'' cabinet (size of the MB150), and my ears could bleed because of those lows. If you have ever tried to play on a 15'' ampeg stack cab (without the complementary 410), that is how low the VS HH bassamp can go.
It means that the precious 150 -500 hz are superbly ignored by HH

. You litterally need to take those out of you bass with your fingers, playing near the bridge

.
(I did not measured those Hertz, it is my years of experience as a bass player that tells me it must be around those values).
I supposed it would be possible to replace the pots by better, modern ones

, that would be an upgrade I'd be ready to do.
The VS bassamp has a Bass Boost switch (on the left), that somehow offers some more definition (maybe around the 150 200 Hz), but not sufficient to compensate the lack of mid definition

.
The Valve sound switch (on the right) definitely adds some valve-ish quality to the sound (more harmonics maybe, that compensates for the highly dry, natural sonic programme of HH design

). But as said before by Moscowbass, if the Gain is engaged over 6 in the red zone (green actually on HH gear), it will produce a pretty psychedelic fuzz, quite wooly indeed (not that it would be comparable with Zvex Wooly Mamoth Fuzz, which I have never tried

). The VS switch adds some compression as well.
The Gain does what it should, but is not useable for a properly defined distortion.
As for the power, I used to play it in gigs in bars (way back then, when I knew nothing about bass tone) on the elephantesque 412 Fender cabinet (aka the Pyramid), 4 Ohms, for several years and I was usually asked by the owners to turn it down. But retrospectively I now know it was probably due to the ridiculous amount of infra bass the audience had to stand

. I probably suffer partial deafness myself

because of those HH lows (not joking). I have read somewhere

that the toroidal transformers used by HH actually makes them quite powerful beasts, to which I fully agree by my experience.
Reliability : excellent. When it stops funcioning, it usually is the 2 easy to find "buttons" components (dont know what they are called really) on the rear panel that are dead. Not even necessary to open the box. And the inside is deceptively empty, the relm of void. What I know about HH amps is that they are robust, made for the road and easy to maintain, as confirmed by the repairmen that dealt with mine.
Prone to hiss as years go by, just cut down the Presence

.
To conclude

, this head does definitely not correspond to the needs of the modern bass player

. HH never was hugely popular amongst bass or even guitars, and only during a short period of time end 70s to the 80s. There is probably a reason for that. Their conception of sound did not match the needs of musicians. But the BBC radio used their gear for studio purpose ...
Just buy one if it is cheap

and if you are curious

, but also because they are quite unusual

, cool looking

amps with wired plastic handles and their green, back lighted panel (pre Trace Elliott somehow) ; and if you want to sound like the Buzzcocks in '77 Manchester

.
Cheers.