The question still remains in taxes. To get into the MBCBP, it typically requires that you hit above the tax threshold for all tax deferred accounts. You can max out the 401K (Roth or traditional, or go Roth, or mega back door, and also normal back door into a R-IRA for yourself and spouse). You fill up those buckets, plus HRA, and now into a taxable situation where excess is taxed in and out. MBCMP allows you to continue in deferral while all the pre and post and accounts are also being filled. To those complaining about pensions lost, I don’t see a loss here. Some get upset- but if you run numbers it can be a great retirement vehicle. Everyone’s situation varies and it can helpful or hurtful in your buckets. Eligibility and opting in should matter as a point, but not a knock to a MBCBP. There is a reason it’s a big deal for high earners.