I taught with OEG for the second semester of the 2018 school year, and OEG was, and still continues to be even a year after my employment with them, a fantastic resource for interfacing with the infamously bureaucratic Thai immigration system. Most recently, I've received help with employment documents relating to Thai immigration, and what is usually a never ending ordeal of paperwork has been made pretty simple on my end with their great approachability and responsiveness. Not to mention that this help is only necessary because I am teaching in Thailand again this year due to my first experience being so great.
For your first experience in Thailand, OEG is the perfect choice because they provide you with an orientation that gets you acquainted with other new teachers and support staff as well as the basics of Thai language and culture. Once you get to your school, OEG provides support which makes it easier to get the necessary documentation to stay and work in Thailand and their support staff, many of whom are teachers here as well, are extremely friendly and helpful with any questions you might have.
Managing your expectations for the school facilities in Thailand is important, but most schools, from what I've heard and in my personal experience, have the means to accommodate any teaching style with enough effort on the teacher's part. If you use PowerPoint in the classroom, computers and classroom projectors are quite common. You will always at least have a blackboard and chalk, but if you're placed in a city you'll almost certainly have more. The school I was placed at had TVs in the classroom as well as a whiteboard and projector, and even air conditioning in most of the classrooms.
Overall I completely recommend this program and had nothing but good experiences in regards to everything OEG provided. If you want to teach abroad and haven't dealt with the Thai employment system before, doing this program is undeniably the best way to go. The initial cost is nothing compared to the information and experience it provides you with, and it makes your future trips abroad much easier to manage.