I'm a brand new DM about to start Tomb of Annihilation with my group. The party consists of four members: a druid, a fighter, a rogue, and a bard. I'm planning on giving each of them a fairly mundane magical item from Syndra Silvane as they are leaving Port Nyanzaru. The PCs do not know that these items respond to the user's abilities. The items are enhanced once they hit level 8, and again at level 16.
As an example, the Rogue will receive a Wooden Pipe, with Sylvan lettering engraved on the side. Once per day, the pipe can be blown into, and a cloud of smoke, encased in a bubble, floats out and moves 20 feet before popping. At level 8, this smoke bubble becomes one cast of cloudkill.
I'm worried that these items could become too powerful, but I've tried to curb this by only allowing them to be used once per day.
What are some potential issues that could arise from having these "evolving" magic items?