I've used this on my phone, ipad and MacBook Pro. My review will reflect all three.I'm currently using this to teach my three year old to read, so my review won't cover the effectiveness of its English teaching abilities.The bugs:Signing in is a pain. While creating an account is strait forward, it doesn't keep you signed in between sessions. It also doesn't integrate with the built in password manager. I can see this being a feature if it were on a public device like a library computer, but I don't know of a lot of libraries that use iPads or iPhones. So most users will just stop signing in.Some of the lessons (like unit one, lesson one) refuse to download to any of my devices. I can get unit one, lessons two and three to work fine, but there are a few lessons later in the first unit that also don't download. I don't recall which lesson numbers, but the one about aliens specifically doesn't work.There are parts of the lessons where they ask you to speak and the computer rates your pronunciation. It seems to base the rating on accents from Europe, so my American accent gets hit or miss ratings. Which isn't a problem. Again I'm teaching my son to read, not to speak. The problem comes in when that feature it's unavailable in some lessons. I'm not actually deducting points for this since it doesn't negatively impact my personal use case, but I thought the developers and other potential users would like to know about the issue.On the phone app, it only plays the audio through the phone speaker. The one where you hold it up to your ear to hear it. Not the one you use when you put your phone on speaker. It even does this when connected to a Bluetooth audio device (headphones or external speakers). I look ahead on the lessons with my phone, but I only teach my son using my MacBook, so this doesn't really affect my usage, this I'm not weighing it into my overall trading. But this issue will likely affect someone else, so I'm including it.The pros:It's free. I'm not paying anything for the early lessons. They may charge for later lessons, but I don't know. I'm sure they monetize this somehow. Everyone has to make a living. Based on how well my son is doing with it, we may choose to pay later if that's a thing.It's fun. Don't get me wrong. I'm not sitting down to play it by myself or anything, but I can keep my toddler's attention for a solid 10-30 min depending on the day. For those who don't know, that's a really long reading lesson for a toddler (your mileage may vary).The lessons that do work are effective.It has variety. Not all the activities in a given lesson are suitable for reading, but that actually helps to keep my son's attention.Creating an account is simple. I know I mentioned that signing in is unnecessarily difficult, but the initial account creation is easy. I wanted to make sure that was noted down here and not just in the cons section. To get around this, you can simply use the app as a guest. Doing so means you can't sync progress across devices, but that's really not a deal breaker for me. I'm using my laptop as the default educational device and using it as a guest is good enough for me.The user interface is standard and mimics the UI of other games (wasd and arrow keys move your character and the mouse selects things)For my overall review, I'm giving it four stars. Granted, there are some significant things that need work, but I'm personally still getting enough value from this app that I don't see those things as detrimental to my use. That may change as we progress through the lessons, in which case, I'll amend my review. But as it stands, for a free app, this is usable, enjoyable and meets my needs. I'll be recommending this as a teaching aid to my siblings to help teach their kids too.