To be honest, you're very unlikely to find clues to the source of your ME via genetic testing, because no-one yet knows for sure. Scientists can't put it any stronger than 'there appears to be a genetic component', and that won't change until an exercise is done involving very large numbers of ME patients. A researcher in the UK is currently planning a funding application to do this work – but it will depend on raising the money, the research will take time, and it may not produce clear results.
Drug reactions are potentially useful if you're likely to be in need of drugs for which genetic profiling has been researched. Many of these are powerful drugs that many of us will never (hopefully) need to take anyway. Adverse drug reactions are very common in ME, but they're unlikely to be based entirely on an individual's genetic profile – some will be secondary to the disease.
There's a lot of online talk about subjects like methylation, and you will get some clues from a genetic profile. Unfortunately, it still won't really tell you all that much. Having this or that single SNP doesn't indicate a specific effect on your health, because there's so much genetic interplay and many traits have highly variable penetrance. It's mind-bogglingly complicated.
I hope this doesn't sound depressing – it's certainly not meant to be dismissive of genetic testing as an area of promise in research. I just don't want you to waste your money on something that may be of limited or no use to you at the moment. Few of us have a lot to spare!