1. Chronically understaffed/high workload. Busuu's engineering department just has too few too small a headcount and you will feel this in the amount of ad-hoc requests you will receive. Earlier in my time at Busuu this was because of high employee churn (as some previous reviewers mention) but this has improved somewhat and now is due to extremely sluggish hiring - which could indicate that perhaps compensation is not up to market standards. I sometimes felt trapped in a negative loop where I didn't have enough time to tackle tech debt because of the workload - which down the line leads to an even higher workload!
2. Erratically fast moving, constantly shifting targets. The culture that leads to minimal bureaucracy and Busuu's startup atmosphere does have its downsides. I think Busuu is often too keen to move onto the next big thing, or to chase the next hot metric rather than learnings its lessons and iterating on what already exists.
3. Tech debt. Busuu is a surprisingly old company and its technology still bears the awkward legacy of some ill-considered decisions. To be fair, its impossible to not acquire any tech debt and the senior tech leadership is pushing initiatives to modernise the tech stack. However, these initiatives are months or years away from completion
As a final gripe, the bonus is a function of overall company performance and is essentially a lottery because you're not going to change the top line performance of the company as a worker in the leaf of the organisation chart.