This circuit has a lot going for it. For one thing, it only consists of two transistors, two capacitors and four resistors. That also means it consumes very little power. You can control the flash rate by changing the size of the 100k resistors (100k makes for a pretty slow rate).
You can also control the duty cycle by using resistors of different values on the two sides. The 470 ohm resistors control the current through the
LEDs. Normally you want to limit this to 20mA, but to conserve battery power, you may need to limit it even further. You can also connect several LEDs in series, instead of using only one for each side. With red LEDs (1 per side) and the values shown, the circuit draws about 11mA.
In the late 70s, National Simiconductor came out with the LM3909
LED flasher chip. Many of the electronics magazines made a big deal about it at the time, and I got one from Radio Shack, experimented around with it and concluded it wasn't such a big deal after all, although I did use the circuit in an LED flasher I took to my first Rainbow gathering. After that, it was never seen or heard from again. I have no idea what happened to it, but I think the fact that it disappeared without a trace shows I had little nostalgia for that chip, or found it useful in any way, although I wish I still had it so I could show people exactly why it isn't that useful.