The main benefit of something common and well supported like VIX is that it's easier to transfer between companies without selling it, which for a brokerage account is a taxable event.

Fidelity has no expense funds or low expense funds, but if they change their mind or the company becomes bad for you, you can't move it to another provider without being taxed.

If you will never leave Fidelity or if it's not taxable anyways (retirement) then it's fine, but if you think you might have to move assets then it's a potential risk unless other providers also support them.

Being trapped is not worth the slightly lower expenses IMO.

Thanks, that helps. In this case, it's my IRA money anyway, but that's good to keep in mind.

If you're fine with 100% risk then probably not, but you want some low-risk assets depending on your age. And if you have high marginal tax rates like anyone living in CA does then a little tax optimization is worth it.

Oh, also mutual funds like FXAIX are less tax-efficient than ETFs.