Some here are of the opinion that lack of obstacle avoidance is not a deal-breaker and that is certainly a valid opinion. I'm usually hesitant to buy any new product until it has established a track record in real world. Spark is a tough little bird as many user reports attest. Mavic Mini, in the quest to save weight, has yet to prove whether its as durable. Certain "teething pains" can be expected with a complex new product such as MM and the early feedback is a mix of pro and con. DJI knew what the Christmas buying season meant when they released the MM. As a Spark owner, knowing the track record of my drone gives me a different perspective than if I was a first time drone buyer. I can only suggest that you diligently research the online communities to see if the MM sounds like something you'd want to invest your money in. It's good to have options and in my opinion, it comes down between Spark and Mavic Mini. Good luck with your quest.
Thank you!