This is a bad idea. We know the problems in using these providers because we are often contacted to fix the errors in their filings! Many of these filings are prepared by contractors with limited expat tax and international tax knowledge. Although you are using a “professional,” the IRS looks to you, not the CPA as bearing the ultimate responsibility for the accuracy of the filings.
Sadly, we have had clients come to us who have already engaged a CPA to correct their filings and are now having to engage us because the corrections weren’t correct. It just doesn’t pay to cut corners.