This’ll be a question on a lot of people’s minds, including mine. I like to run the beta whilst I have Apple’s attention. This means that when you raise a radar you’ll at least get a response. Depending on what we get with Reminders it’ll be a good opportunity to test and raise anything you’re not happy with. For me I will be running it but which device will be on is the biggest question. I think my 10.5″ will be the test device this year. If my main iPhone gets it will depend on what dark mode looks like and how good Reminders is. I’m also thinking about testing CarPlay this year so I’ll have to put it on there.
If you heavily rely on your iPhone it goes without saying you should avoid the beta for a while yet. Maybe jump onto the public beta that’ll come out most likely the end of July.
If you don’t rely on your iPhone for travelling and mission critical stuff then go ahead but don’t expect your experience to be as good as iOS 12 and some of your third party apps will most likely break.