As a buyer, you can meet with as many loan officers as you want. They each will ask for information from you to verify income and assets, and then can issue a pre-qualification or a pre-approval letter.
This letter isn't really worth having. It basically states that the buyer applied for a mortgage and that's all. If it states anything else, it usually will say that it is subject to verification of income and assets. I have had buyers that were pre-qualified, and when we went to write the purchase agreement, their mortgage company turned them down. We then had to shop for a new mortgage product to continue the purchase. Being in this situation adds unneeded stress and worry. It's just smoother to get pre-approved up front.
This letter is really the minimum that you should use during the home purchase process. It means that you have applied for a mortgage, and that they have reviewed your credit scores, verified employment, verified your expenses, and verified your assets. If there are special concerns with your file, they can talk with the underwriter to gain clarification as well. Anything less than a pre-approval letter isn't usually worth obtaining.