I've been using Colab for over a year now. I train deep learning models on NLP and medical imaging datasets.

It's a great tool and it lets you focus on the code and the models, instead of the hardware and OS. But $9.99/month is a little expensive for my taste.

You can't customize it and if they change something you have to install software by hand sometimes. It should be $1.99/month, that's the kind of price I'd pay for this basic cloud computing service.

edit: I use Colab to play with ML models. I really don't think it's possible, for instance, to train a model on Imagenet using Colab. So Colab is similar to the microwave, if you want to cook a serious recipe you should use a real kitchen.