The latest update of this application was released on Jun 20, 2019 and IDM Lite has been installed by over 100K users. Ads are a part of the app. A free .apk file of IDM Lite 3.9.1 is available from Droid Informer and you can have a look at users' reviews on this site. Prepare 10 MB of free space on your device for this app setup package and take into account that it works fine on Android 4.0 and higher.
According to the users’ comments, you can notice such a disadvantage of the app as aggressive ads.