I have an emmeti installed. It's been there for 7 years and still functioning okay. I don't know whether it's the best brand, but it's not "unbranded" so that's something. The auto vents are rubbish though, they leak - so I've replaced them with a short length of copper pipe with a manual vent on top.
There are loads and loads of different type and levels of quality, so the internet can be your friend here, go and do loads of research and read through reviews etc.
Pro's usually find one brand and stick with that as it suits their needs and meets their standards. Sometimes that may not suit a DIY'ers needs or their budget.
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