I use a Sigma EF-610 P-TTL flash and wouldn't want to be without it, there are a couple of things to master but it can get perfect exposures automatically thereafter every time. However, I can also do the same with a 35yr old Nissan 360TW auto thyristor flash. Yes, I can only use up to 3 aperture settings and it's not as powerful as the Sigma, but it works auto-exposure fine. Using bounce off the ceiling or wall with either can make life a lot easier than dealing with very low light (noise and slow shutter speeds/subject motion blur) and the results look a lot like natural light.
I bought a second 360TW for the princely sum of £15 off the bay 2-3yrs ago. It's got swivel/bounce and a switchable fill flash. There's plenty of other auto-thyristor flashes around but you have to make sure they have a low trigger voltage, some old ones for film had 300 volts on the contacts which can fry a digital camera. There's a website that lists trigger voltages, keep it under 10.5v (the Nissin) and I know it will be fine - no issues here since 2006.
trigger voltages
You should be able to find guidance on using an auto thyristor flash on the web, but basically on the Nissin you have a switch with 3 power settings and these relate to fixed aperture settings on the camera. To start with, stick to either ISO 100 or 200, put the camera in M mode, set the shutter speed to 1/160s, choose one of the 3 power settings, then play around with your aperture taking indoor shots with the flash head pointing up. Once you've found an aperture that gives good exposures, that's it, that's the aperture for that power setting. Then repeat with the other 2 power settings. Now you have 3 apertures where exposures will be right automatically at any distance (within the range of the flash). Put a sticker on the back of the flash to remind you of the apertures for each of the 3 switch positions. Done.