I have participated in two clinical trails. My experience was good in each. On one trial, I felt like I had an especially good rapport with the physician in charge... which was a plus. I got extra screening, extra time with the doctors, interacted with fellows (doctors in the advanced stages of post-MD training) so I felt like I was contributing to the future of medicine, and was able to contribute to the development of drugs that might save lives (one turned out to be a blockbuster. I was in the arm that didn't get it, but I can still say I contributed!)
Reality checks: not all drugs/treatments/trials work (for you) so keep expectations realistic. Carefully assess how cooperative your insurance will be about covering certain costs. If a drug company or equipment manufacturer is running the trial, in most cases, they will pay for the majority of costs. Sometimes, there may still be some expenses (routine labs, imaging that would need to be done anyway) that are the patient's responsibility. If you have insurance, it should cover these costs, but it is best to get approval in writing in advance. Participating in a trial can take additional time and effort on a patient's part... so get details about what to expect and plan accordingly. It might even result in some additional expenses - like if you need to travel. But some trials have a budget to help with those costs, so if they are a concern, be sure to ask.
A critical piece on information I think people need: it is *never* ethical to withhold treatment from a cancer patient (at least not without their consent). Many people have told me that they would not consider participating in a clinical trial because they are afraid they would be given a placebo... in other words, not be treated. This will never happen without your consent in a legitimate clinical trial. Don't assume the worst and rule a clinical trial out before you give it fair consideration. Some trials assess how the standard treatment compares to the standard treatment plus a new drug. In a case like that, you might get the treatment you would get anyway - they just want to monitor you carefully to see how your arm of the trial compares. You might get the arm of the trail that involves the standard drug plus a new drug. Were the results better? Or perhaps the new drug made no difference. Sometimes trials assess a new treatment technique or equipment (like radiation delivery methods or machines). Without the information these trials generate, we will never make progress in our struggle to outsmart cancer. You have to do what you think and feel is right for you, but it is worthwhile to consider clinical trials.
NIH maintains a registry of clinical trials. You can find it here: https://clinicaltrials.gov/ And https://www.breastcancertrials.org/ features clinical trials specifically for breast cancer patients.