This is definitely a painful experience. Will you be able to swap it out with the seller? The Metropolitan is a pen that just has to work out of the box without any tinkering.
The Cavalier should have a good cap seal - so there's no danger of it drying out if left unused for a few weeks. But, even if you find it has dried up, there is nothing to fear - just flush it out with water till the water runs clear, shake it (like you would an old-time thermometer) to remove any excess water, and let it air dry. Then you can ink it up and you're good to go.
I buy from different online retailers. If you don't mind sharing which country you are in, the community can make recommendations :)
Hobonichi notebooks and planners are all Tomoe River. So are Endless Recorder notebooks. Galen also has notebooks in TR. Now is a good time to get TR - it is still available in many places :)
As long as you don't let the ink dry in your fountain pen, you should be fine. In a fountain pen with a properly sealed cap, that should easily be several months. I recently opened a Pilot V pen that I hadn't touched since 2020 and it wrote on the first try.
If you can share what pen you are using, maybe we can give you a better answer than "It depends" :)
Tomoe River 52 remains a top favourite - I have a couple of notebooks left, so should have it for a while. Have a couple of TR68 notebooks as well.
Cosmo Air Light is a close second - brings out ink properties beautifully and can take a lot of abuse.
The best value for money I've found though has been the Nakabayashi Logical Prime notebooks. The paper is fantastic, and the notebooks are priced decently.
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