I'm just wondering if I can use the cheaper amazon chargers, or if that is somehow dangerous to the DJI Spark. I'm gettingg mine in 2 days, but did not order the fly more bundle. I want to charge my batteries quicker, but I need to know if off brand charging hubs work okay.

We would recommend users use the original one to charge their spark as the third party accessory is not tested. Thanks for your support.

It’s probably ok.
The worst thing that can happen, is that the battery gets more than 13.05 Volt when full.
If you have a way to check for that, no worries.

When it comes to the batteries on the spark I wouldn't use off brand. Since you have already bought the charger then I would recommend keeping an eye on the batteries until they are fully charged. Once fully charged immediately pull them out and you should be good. If you leave them in too long they will likely lose charge capacity. Also, if you don't plan on using the batteries for a while its recommended to store them at 1/2 capacity to keep it's charge potential in optimal condition. Fly safe!