Is this really true though? I have kaiser I think silver marketplace plan. While they did cover a good chunk of a semi-recent hospital cost (out of state emergency with no Kaiser in the state). I'm still getting new bills that Kaiser won't cover. But maybe I don't know enough to file complaint/forms to push back

Yes it’s true - if you go to their facility no out of network bills. You may still end up w a bunch for different services but all considered in network. If you have an high deductible plan you'll still pay that whack. If you have gold / platinum no deductible plans you'll pay your co-pay.

You CANNOT go out if network though - that's really the deal / tradeoff.

If you travel a lot, have a fav specialist etc may not be a good fit - a national ppo may work better or us within us coverage for specific trips. Generally you can get $100K coverage for trips > 100 miles away from your home + 1 night away from home as part of your insurance package (exceptions related to traveling for medical work, getting drunk and hurting yourself etc).