Hi, I am sorry for a very newbie question, but I have never used an external flash before.
Can someone tell me, in fairly simple terms, what the FL300r flash will allow me to do and will not allow me to do?
I mean compared to the pop-up flash, and also something more powerful like the FL36r.
Also, is it fine to use on lumix cameras like GH1?
Mainly I just want to get a flash to experiment with different kinds of photography.
Note, I haven't seen the FL-300R in person, this is from the specifications.
The FL-300R sits higher that your pop-up flash, which means it is less likely that you will get red-eyes in humans and green-eyes in dogs and cats when you use the flash. I'm guessing here, but with the pop-up flash you likely see red-eye if subjects are about 2 feet away from the camera, and with the FL-300R, maybe about 5 feet. The FL-36R is taller still, and that range is probably 8 feet.
In addition to straight on shooting, you can angle the FL-300R to 30 or 60 degrees. This allows you to bounce light off the ceiling (at 60 degrees) or illuminate macro shots from a different angle. The ceiling bounce will only work when you are shooting in landscape orientation (i.e. normal orientation where you are more interested in wider pictures than tall pictures). Using a ceiling bounce means that you don't have red-eyes in general, even for people further away. Because the light is bounced off the ceiling, it is spread out, which means the shadows are more diffused while using the flash straight on or the pop-up flash, means the shadows are more harsh. The FL-36R can tilt and swivel in just about any direction, which means you can change the angle of the bounce. You can also shoot in portrait mode, and using swivel, do a ceiling bounce.
The FL-300R is more powerful than the pop-up flash, so that you can take pictures of people further away. The FL-36R is even more powerful than the FL-300R. Note, when you are doing bounce, diffusion, or other flash modifications, it eats a lot of power, so having a more powerful flash means you can use the modifiers. Note, there is no getting around the falloff rule for light, which means if you take pictures in a large room with the flash fired straight ahead, and have people in front of the subject you are shooting and behind, the people up front will tend to get over-exposed, while the people at the back of the room will get under-exposed. In some rooms, you can angle the light for a ceiling bounce, so that the distance from the reflection on the ceiling to the subjects is roughly the same.
The FL-300R has a wide angle diffuser on it which means you can use the flash to shoot if you have the 9-18mm lens installed. The FL-36R has a similar diffuser. The pop-up flash can only illuminate at 14mm or longer.
The FL-300R flash only supports Olympus and Panasonic cameras, and it has no options for manual support. It does have the remote flash support for Olympus DSLRs that support it, but there are restrictions in its use. I know that the XZ-1 cannot drive the FL-300R in remote mode, and I wouldn't be surprised that the older Pens or DSLRs may also have limits on remote flash working. The pop-up flash being on the camera can't be remote from the camera, but you need the pop-up flash to drive the remote flash support. If you anticipate ever using the flash on other cameras in manual mode, or do a strobist style manual flash setup, get the FL-36R and not the FL-300R.
Neither the FL-300R nor the pop-up flash can be used with a shutter speed faster than the camera's native sync speed (1/160 to 1/250 depending on the camera). For indoor shooting, this is generally not an issue, as the flash will stop motion of the subject illuminated, but outdoors in bright light, it means you can't use the flash to fill in the shadows and make the light less harsh, because the camera needs to use a faster shutter speed for the picture, particularly if you use a fast lens and want as small of a depth of field as possible. The FL-36R has a mode called FP-TTL that allows you to shoot at a fast speed.
The FL-36R also supports the older 'auto' mode. This is the original flash automation. In auto mode, the flash is told what aperture you are shooting at, and the flash uses its own sensor to figure out when to cut off the light. This is useful in some cases, because there are people with really fast blink reflexes, and the normal digital camera flash which does a pre-flash to figure out settings, causes people to start blinking, and when the main flash comes along, their eyes are already closed.
The FL-36R uses 2 AA batteries, while the FL-300R uses 2 AAA batteries. I imagine you will need to replace batteries more often in the FL-300R. There are other flashes that support the Olympus camera which use 4 batteries, and these will last longer than the FL-36R. The Metz flashes and the FL-50R tend to recharge much faster than the FL-36R, which is useful if you are shooting something like a wedding and need to get a few flashes off as the bride runs down the aisle.
My take away is if you want a flash you can learn about various techniques, get the FL-36R. If you want a light weight flash to give you a little help, go with the FL-300R. If you need faster recharge time go with the Metz 50 AF-1 which is roughly the same cost as the FL-36R, but it doesn't have auto mode and is much larger. If you really need to crank out the shots, get the FL-50R or Metz 58 AF-2. I put together a list of various 3rd party flashes for Olympus and Panasonic:
http://www.the-meissners.org/olympus-flash2.html 
