Resort Airline Check-in (which technically is a separate service from Disney's Magical Express) has been around for more than 5.5 years, and it's very reliable as evidenced by the fact that there are not widespread complaints of luggage not arriving back at the home airport.
As noted above, the luggage must be taken to the RAC desk in your resort, you can't just leave it with Bell Services or leave it in your room. Also as noted above, the entire transaction MUST be completed no later than 3 hours before your scheduled flight time. If it's 2 hours and 59 minutes before the flight, the computer won't allow the transaction to go through, and you won't be able to use RAC. It's not like the staff can makle an exception for you.
Think of RAC as curbside check-in, because it exactly is curbside check-in, except that it's in your resort lobby rather than at the airport. Exactly like curbside check-in, you must present ID, you check in for your flight, you get your boarding passes, and you check your luggage through to your final destination (which means you will no longer have any access to it).
Ans also, just like curbside check-in, it is customary to tip the staff assisting you. The people staffing RAC are not Disney cast members. It's also important to realize that the RAC cast members are not in any way related to Disney's Magical Express, which means they can't answer any DME questions (such as bus questions and so on).