I own both. I used a flower for years with not a single problem. It's probably one of the most reliable pieces of equipment that I've fished with over the years. However, it is also one of the most dangerous pieces of equipment that I've fished with over the years. Because I'm bringing my seven year old son nowadays, I picked up the Big Buddy this year, for safety reasons.
I had the same thoughts as nubote regarding using a rechargeable battery instead of burning through D's. Big C in Rogers sells a 6V rechargeable battery for $14.99 in their game feeder section. My float charger does both 6 and 12 volt, so no added expense there. I struck when they were on sale for $9.99, and by using a $10 off coupon that I received in the mail, I picked up my 6v rechargeable for $.64 after tax.
So far I'm very happy with the cleaner & quieter burn of the big buddy. I hope to get many trouble free years of service from it, but my flower is still there in case I ever need it.