Stay on COBRA or move to new employers insurance (North Carolina)

I was recently laid off from my employer of 6+ years and as part of the severance they are giving me COBRA at no out of pocket cost for 6 months. I was lucky enough to get a new job within a week of getting laid off from my previous employer. My new employer's health insurance starts on June 1st, and my previous employer is paying for COBRA through the end of October. The new employer covers all of the health insurance premiums, so there is zero paycheck deductions, but the coverage at my previous employer is better. My new employer has said that they will pay me the amount that they contribute for health insurance to me if I decline their coverage (even if it is temporary).

I had the idea of staying on COBRA through the end of year as I have a serious (could be expensive) medical condition and don't want to risk something happening and having to start my deductible over from scratch. I've calculated my COBRA cost based off of my premiums, and the numbers on last year's tax return, and it would cost me about $600/month to continue COBRA after October. I don't know the exact amount that the new employer would pay me, but the boss estimated it would be at least $300/month. If I estimate off of this amount that would be a total payout of at least $2,100, which would more than cover the $1,200 cost for COBRA for November and December.

Is this a smart idea, or are there any downsides to this plan that I'm not thinking about?