What does the company do well? 1&1 are one of the legacy domain registrars, which likely instills trust and brand recognition among their (many?) customers.
What does the company not do well? Not much innovation has occurred over the years. Pricing is abnormally high and attempting to remove (transfer out) a domain can be a tedious process. Still not the worst experience in the industry, but not great.
What do you wish you had known about the company before using? Nothing. I did my homework. I had registered domains during a promotional period (for cheap) and knew they would be renewing the following year...not cheap. I was prepared to transfer the domains out in time.
Have you used a competitor to 1&1? If so, how does it compare? Yes, just about every other registrar except Network Solutions is likely better in scope among all attributes.