One of my players has a Warlock with the Pact of the Chain. This PC has a quasit familiar. If we are applying the rules correctly…
Pact of the Chain
You learn the find familiar spell and can cast it as a ritual. The spell doesn’t count against your number of spells known. When you cast the spell, you can choose one of the normal forms for your familiar or one of the following special forms: imp, pseudodragon, quasit, or sprite. […]
[...] While your familiar is within 100 feet of you, you can communicate with it telepathically. Additionally, as an action, you can see through your familiar’s eyes and hear what it hears until the start of your next turn, gaining the benefits of any special senses that the familiar has. During this time, you are deaf and blind with regard to your own senses. As an action, you can temporarily dismiss your familiar. [...]
VARIANT: QUASIT FAMILIAR [...] Familiar. The quasit can serve another creature as a familiar, forming a telepathic bond with its willing master. While the two are bonded, the master can sense what the quasit senses as long as they are within 1 mile of each other. While the quasit is within 10 feet of its master, the master shares the quasit's Magic Resistance trait. At any time and for any reason, the quasit can end its service as a familiar, ending the telepathic bond.
… then he can communicate with it within 1 mile and see what it is seeing.
For example, in a mission where PCs have to peek at the enemy camp, he could just stay hidden and send the quasit exploring the camp. The quasit can turn invisible and polymorph into a centipede, so it can go anywhere (even inside a building), and the Warlock can see everything.
Now, is this correct? It would seem really overpowered to me.
If it's correct, how can I limit this power in an acceptable way?