We have had good success with Pootle Page Builder and Jamie Marsland has provided great service from across the pond. Currently, we are reviewing the Divi Builder and find it remarkably vibrant with a longer learning curve. There does not seem to be any SEO or performance issues with either. We are hosted at WPEngine and the load times are superior with both builders I have mentioned. By way of experience... getting good with one or two builders is advisable and jumping around will create additional labor costs. Plugin conflicts can also be an issue.