I have an Aqua-Flame unit, which is very similar to a Microflame.
John is correct in stating that the flame is virtually invisible. Fortuitously, the ratio of oxygen and hydrogen produced is just right for burning, and doesn't have to be changed, but, although the flame is very hot – approaching that of oxy-acetylene – it is relatively low in energy. To counteract this, it has something called a booster tank.
Output from the generator is fed through the booster and then to the torch. A liquid is placed in the booster to achieve two things, a) to counter the effects of a blowback, and b) to change the flame temperature. If the booster contains water, then pure oxy-hydrogen is burnt, but if it contains a suitable chemical, the flame temperature and calorific value, is changed. I use methylethylketone (which, I believe, is used in dry-cleaning) to reduce the temperate to about 2000C and increase its calorific value.
Flame size is determined by the size of the torch tip, which is rather like a hypodermic needle, and not by a regulator valve. The flame produced ranges from about 3-4mm wide and 80mm long for the biggest tip I have, to about 0.5mm wide and 2mm long for the smallest one. I am able to hard-solder the tiniest chains with the small tip.