It does not allow for customization to the extent needed. Not all businesses are subject to the same sales tax rules in every states. They don't have options to exclude yourself from certain taxes like the B&O tax in WA when using their automatic filing system. Until recently you could not change if shipping was taxable or not based on your particular business situation.
They also don't fully integrate with Shopify, meaning they can take the information from Shopify, but they are not the ones calculating the sales tax at checkout, Shopify does, and Shopify does wrong a lot because they use zip codes instead of addresses. Also, when doing refunds, more often than not tax jar records them wrongly, so I have to download the file, fix it manually, and re upload it. Not very friendly. Also, the refund ID is different than the transaction ID which makes it harder to find the original transaction to then go to Shopify and see how the refund was done.
Their customer service is good but slow, too slow sometimes given that some things are tax sensitive.
They only solve one issue of the problem, calculating taxes right, but the other half, having the filing done correctly, I can´t do it, because their system makes me over pay for taxes due to the lack of customization and exemptions I can apply if I file on my own. Review collected by and hosted on G2.com.