I bought one once. I was unimpressed. When it was windy, it was cold and turned into a sail. If you have one which is waterproof, then the fabric will rustle, which I found annoying. When I used it in the rain and then packed it away, it was wet and bulky. I had to have another jacket as well as the poncho for the wind.
On a budget, I would wait for jackets in the middle of Lidl or Aldi. You can get something for £20-30 which will be close in performance to much more expensive jackets.
I like Paramo Alta jackets. I bought have bought a couple from their
outlet on eBay. They aren't cheap, but they are really comfortable. Its really adjustable, with velcro and elastic cuffs, so you can seal them up its cold, but still look at a watch. There are zips under the arms for more ventilation if you're getting hot.
The fabric is breathable. You can reproof them with Nikwax Tech wash and TX Direct.
The outer layer of the fabric absorbs a bit of water. That means in a shower you don't get a dry top and a soaking wet band at from the water that has run off the jacket. In heavy rain, you need overtrousers. In prolonged heavy rain you also need waterproof boots.