1st Migration

Hi there, 
We’d like to answer your questions below: 

For the 1st migration, is it safe to run it directly from the LIVE website to the TEST migrated website ?

Yes, our migration tool just reads only, thus it’s possible to migrate directly from your live source M1 database. 

Can this somehow hurt the LIVE website during the migration, or slow it ?

Since our migration tool is just an end-point, thus MySQL server can handle well with almost no effects to your live server performance. 
Anyway, there’s a few notes under your circumstance: 

• If you have a separate database host, you must enable a remote MySQL database connection to your Magento 1 database following this guide. 
• It’s a better option in terms of migration performance if you connect directly to your databases in the same MySQL server rather than via a remote connection. 

Hope that helps. 
Regards,
Ubertheme team