Don't waste your time! The app is free but not doing any good as the customer who subscribes to your store doesn't actually go on your subscriber list, I've reached out to support and he advised me he fixed it . The next day it was the same issue. he asked for access to my store and said he will get back to me within a day but when he contacted me saying it was fixed I saw on my store he had never logged in & told me to manually add them myself . Such a waste of time now i have to get another app!!!
Thank you for bringin this here i aggree that there was an issue where your subscriber was not getting added to your shopify admin customer list but as this was a global issue that was faced by every client therefore we corrected this globaly and that is why we found there is no need of login into your store as our developer tested this via his development store itself where he performs the tests.
Also, The same Issue was face by our client "www.jewellerynest.com" you can see the review given just before your review. I know initially this has been frustrating for you that the feature was not working but ignoring the efforts made by my team and saying the app is of waste is something I dont agree as there are many other apps in shopify which do charge you for but do not offer exactly what customer asks and provide 24 hour support as my team do.
Therefore, I request if you can check again the feature I am sure it is working now.