There's a few small details that really bother me - the first one that springs to mind is that you can't customise the text that appears when you send a receipt of payment received. You can edit it, but there doesn't seem to be a way to permanently change the default wording. For receipts the standard wording is:
Here's your payment receipt for Invoice ###, for £##GBP.
You can always view your receipt online, at:
If you have any questions, please let us know.
I find this infuriating because A) the wording feels clumsy ('you can always view your receipt online'?) and B) it really doesn't match my business's branding at all. As a photographer I write in the first person ('me' and 'I', not 'we' and 'us') and in a much more informal, friendly tone. So having to delete this and type something by hand every time is infuriating when dealing with lots of payments!
The fact that minor detail is my biggest complaint is testament to the quality of the free service, mind. My other concern is that as a free-to-use service, there's the slight fear that they'll one day decide to withdraw their service, or change the pricing entirely, if they're not making enough profit with their current model. Their Wave Plus is an intriguing model (plus taking a fee for card payments) but i have no idea how sustainable it is, for all I know they might be just trying to elevate the company without turning a profit so they can sell it to an investor. As much as I like having a free service, I'd happily pay a small fee, maybe £50 a year or something, just so I've got the rights of a paying customer.
One other minor thing, is I don't necessarily like that I have to add every customer before using them in an invoice. Much of my work is basically one-off (weddings for example) and I don't need a huge long list of clients that I'll never contact again. Review collected by and hosted on G2.com.