I have GSTIN, and if I purchase Book Keeper, Will I be able to claim GST

Yes

Kindly make sure, while registering on website, you provide your GSTIN. (Only GSTIN is mandatory, not the company name)

http://bookkeeperapp.net/registration

After registration, you can purchase any plan on website. You will get invoice on your email from Book Keeper team mentioning your GSTIN.

Kindly note:

• Invoice once issued won't be changed. Kindly verify your details on website before purchasing. http://bookkeeperapp.net/log-me-in/
• If you have provide wrong GSTIN, you wont be able to claim GST
• If you didnt have GSTIN at the time of purchasing Book Keeper, you won't be able to claim GST later (if GSTR1/GSTR3B for that period has been filed already)
• If you have misplaced invoice, you can always request for duplicate copy of invoice
• Invoices will be sent over email, no hardcopy will be sent. Also, all the invoices are computer generated, so no signatures are required.
• If you purchase Book Keeper via Google Wallet or iTunes, you won't be able to claim GST. You will get invoice from Google/Apple.