Meditation apps can be very effective, especially for beginners. This is because meditation apps usually have a large amount of guided meditations, which are a great way for beginners to get into the habit of meditating, but also for more experienced meditators.
Many of them also have meditation timers that you can customize to your preferences, and other options such as meditation sessions with different background sounds that you can choose from.
Many of the meditation apps are also community based, meaning, there is a community that uses the app, and in that community you can read other people's experiences, questions, answers, and share your own.
A big reason why meditation apps are so effective is because beginners who are just getting into the practice of meditation tend to overdo it. Instead of slowly getting into it by starting with short sessions, they start with long sessions which they get very bored with, and eventually stop meditating.
Meditation apps usually have courses, and structured practices made for beginners, for example, the first few sessions will be 5 minutes, and as you progress, the sessions become longer and explore other types of meditations.
Having a structure, especially when starting out, can make a huge difference in the effectiveness of the meditation practice. And this is where meditation apps excel.