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I'm thinking about making a macro photo setup with many light sources (up to 10). It's not viable to buy 10 flashes, even cheap ones. It's more viable to buy 10 cheap lights, but it would lead to such problems as overheating, less natural colors, potentially softer photos due to vibrations (from vehicles passing by, etc).
Another alternative that I consider is using flashes + mirrors as "flash-multiplexers". I never tried it and I'd like to read some opinions about my idea.
Mirrors are going to make the light more of a point-source, as it's 'twice' as far away, therefore more parallel. You'd also have to be quite precise in their placement.
It would probably be cheaper, less prone to breakage & just as effective to use sheets of card, white or silver fabric reflectors or reflective "polys" [big pieces of polystyrene used as reflectors]. Each would be a diffuse light source, still further away than the initial flash, but far less directional.
Since you plan to take macro shots, a folded piece of paper just outside the frame might be a huge, soft light source compared to the object in the picture.
Here's an example:
And the resulting shot:
Note that putting light everywhere might result in a bland picture. You might want to experiment with black sheets of paper, in order to choose where the light doesn't land.
Before you buy any more equipment, I highly recommend you take a look at "The Best of Dean Collins on Lighting".
It's a treasure trove of information about lighting. There's an entire DVD with professional shots using only one light, and many DIY modifiers.
Optically, a light in a mirror is the same as a light directly shining on the subject. As Tetsujin says, they will however, have a higher effective distance. Whether this is an advantage or disadvantage depends on the situation and your taste.
Also repeating points in Tetsujin's answer, but (hopefully) expanding: the purpose of mirrors is to reflect at an exact angle, and create coherent images of the things reflected. You just want a reflection; for most purposes in photography, a coherent image of the light source is not needed and in fact a drawback. Since mirrors are more expensive than most reflectors, you're spending money preserving something (namely, light sources that are close to point-like) that you probably don't want to begin with.
Remember that all sources are reflectors, mirrors are just image-preserving ones. A white sheet acts like a mirror and a lamp shade at the same time. You do have to make sure the albedo is reasonably high, and you do have the inverse square law applied twice, but other than that, any surface can supply illumination. Also keep in mind that two surfaces that both look "white" can have slightly different spectra as far as what albedos they have at different frequencies, and your camera doesn't necessarily see color exactly the same as your eye does.
If you want more professional reflectors, you can do a web search of "photographer reflector". Basic ones will be
