My answer below is based on secondhand knowledge from online research which in my case includes a bit more of an interest in older bayans.
xocd post_id=57424 time=1524317778 user_id=2246 said:
After looking at bayan images out of a google search I am wondering if the typical Russian bayan left hand has no registers?
Bayans can be classified roughly into two groups: standard and concert. The former is more for the ordinary folk (like the AK-47 of bayans) and the latter, as the name suggests, is more for formal/classical concerts. Its not necessarily a matter of quality, but rather of simplicity and sound range.
Your typical/standard bayan will have no register switches at all - neither bass nor treble. These are
predominantly dry-tuned MM on the treble side and 4 reed banks on the bass side. You will occasionally come across a standard bayan with some switches on the treble side, but those are the exception, not the rule. They were probably some kind of gateway instrument leading to the big concert instruments. Example:
Generally speaking, if you dont have a lot of choice in right hand registration, there isnt much point in allowing different left hand registration.
When you come across a bayan with a single switch on the bass, its very likely to be a converter. Having a converter, however, does not guarantee having a lot, or even any, treble switches.
Here are two examples:
Register-less converter Rubin:
register-less converter Yasnaya Polyana:
On the other hand, the high end concert bayan has many register switches on the treble side. Modern ones will also have chin switches. In this category youll find the Akko and Jupiter mentioned by Paul and Geronimo.
Not having register switches should not be seen as making it a toy or
necessarily a beginners instrument (as might be the case in European instruments). Its just a
simpler instrument with a more predefined/characteristic sound. Without getting into bayan ontology again (weve had topics before), you pretty much get only a classic bayan sound and thats it.
xocd post_id=57424 time=1524317778 user_id=2246 said:
How would that affect the way one manages balance between left and right hands?
With the standard register-less 2/4 bayan it is balanced from the outset. Theyve been making them like that forever, so Im sure theyve achieved their preferred balance - which might not necessarily be to the tastes of those used to European instruments.
Also, there is that typical rougher bass sound which I imagine is preferred as a general characteristic of the bayan. Besides complicating the mechanics by introducing all possible combinations, you are also likely to water down that characteristic sound. It might be the case that by breaking up a bayans bass into its parts, it just might not sound as good.