There are many, many success stories for DE treatment abroad. Overall, the costs are lower, but in most countries the donors are mandated to be anonymous, meaning you will have limited information about them (generally you can make specific requests that the clinic will try to honor, and they may try to match blood type and your general hair/eye color characteristics).
Overall, the success rates tend to be lower than the best clinics here in the US (for example 65% abroad vs. 85% at top clinics here). Just like here in the US - unless you have immune issues or sperm or uterus issues, about 90% of DE patients will bring home a baby within 3 fresh cycles.
Many of the top clinics abroad do have waiting lists of several months, but some don’t. You will find the most popular clinics tend to be in university towns where they have access to healthy young potential donors.
The clinics that offer a guarantee of embryos to transfer generally look at it as it is their responsibility to make sure the donors are well-selected and will produce quality eggs. So, they are willing to take the risk and guarantee the two embryos (or offer a discount or return treatment if they cannot do this). I think that makes them even more careful about choosing donors that are healthy and will produce good quality eggs - since they are at risk if the donor does not produce eggs that develop into quality embryos. So, I see that guarantee as a very positive thing.
Overall, due to the lower cost of overseas treatment, it makes DE IVF affordable and accessible for people who otherwise may not be able to continue fertility treatment.
It is best to go in to it with eyes wide open and ask lots of questions. You may want to check out my blog: IVF Traveler for more about traveling abroad for treatment. Good luck!