Yes, they are unsecured, so it is a risk.
I was able to take advantage of one for a short period of time before retiring from mega-corp. I essentially deferred an entire years salary minus what I needed to max out my 401k contributions (and also leverage mega-corp's match).
If you think your employer will remain solvent, you should reconsider the plan. By doing so, you can spread out that high pay over the ten years after you leave, which (given your desired to FIRE) may be at a much lower tax rate than now. At 450K, you are in the 35% marginal (federal, joint). If you bring your 2018 pay down to a measly 165k
you can bring your marginal rate down to 22% (federal), resulting in substantial savings. One possible wrench in this is that you will have higher earnings (in terms of FAFSA). In my case, I was doubtful given my pension and assets whether my child (now 15) would be eligible for financial aid regardless of what I did.
When I was doing this, one of my rationalizations was that executives of my mega-corp would do *EVERYTHING* in their power to pay out on 409A plan obligations. Why? Because their 409A payouts also depended on it.