We have both Amplitude and Google Universal Analytics implemented on our mobile app and web. Both of them are implemented via Google Tag Manager using their respective JS SDKs. I understand that both Amplitude and GA are two different tools but here are the numbers for sessions and users
Sessions
Amplitude - 49K, Google Analytics - 57K
Users
Amplitude - 34.8K, Google Analytics - 39.7K
NOTE: Even though the sessions and users are widely different, the number of ecommerce transactions are same on both Amplitude and Google Analytics.