Juniperus virginiana, eastern red cedar, ERC for short. They get "dogged" by many more seasonsoned grower because they have "issues". There are thousands of them everywhere east of the Rocky Mountains. And thousands of bonsai hobby growers have tried their hand at training ERC. Despite thousands of attempts, there are only 5 or so "exhibition quality" ERC on the show circuit. The reason is that thousands of hobby bonsai growers eventually put their ERC on the burn pile. They are frustrating to work with. Now, it is true, that a small handful of artists successfully create bonsai with them. But these small number of successes is vastly outweighed by the huge number that end up on the burn pile.
It takes forever to get the foliage to form dense foliage pads. They are very prone to a fungal infection, cedar-apple rust and related cedar-quince rusts, and cedar-pear rusts. As many as 60% of the ERC will eventually succumb to the rust. Once the tree has the rust, it is difficult to get rid of. Mancozeb has some effectiveness, but the infection is systemic and persistent, difficult to get rid of.
All those reasons are part of why people end up composting their ERC.
But, if you find one with a nice attractive trunk, there is no reason to not try. It is a right of passage. Every new to bonsai in eastern North America ends up trying one or more. And most, but not all, will put them on the burn pile. Those that don't put them on the burn pile, often end up with a really nice specimen.
Do yourself a favor, at the same time you start with a ERC, get yourself an 'Itoigawa' or 'Kishu' shimpaku juniper. Raise them side by side. In 5 years, you will have a really nice shimpaku. And, you will see why you see so few ERC at North American bonsai shows.