We just completed a two week stay on Bonaire and opted to splurge on UDT. Yes, it was expensive. That said, it made our trip much easier. We did have another couple with us, so splitting the charges made it easier (we only charged the other couple half of what a regular rental would have been since we drove the decision). Was it worth it? For us, yes.
1. We are not exactly spring chickens anymore - the side mounting of the tanks saved my back.
2. The lock boxes just made life easier as we didn't have to worry about what we brought with us. It was my 7th trip to Bonaire, so I was used to bare-bones travel. It was simply easier to bring my coffee mug along, extra lenses/ports, a safe place to lock up my glasses, etc. We've never experienced a theft issue on the island, but the lock boxes made life easier and I'm all about that at this stage of my life...
3. The mat made changing in and out of wet suits/skins/boots easier and much less sand in gear.
4. The rinse hose was great. I, too, have loaded the back with 2 liter bottles filled with water. First, you have to drink the 2 liters, then build up enough of them to last through two dives rinsing cameras, face, etc. Then there is the plastic the island has to deal with. I've also traveled with refillable shower bags - that worked until they didn't (~2 trips). Again, the hose just made life easier.
5. The totes worked great. Thought they were a bit small at first, but we adapted and they worked out great for both organizing gear during the day and rinsing the gear back at the condo/dive center.
Overall, we found the truck to be very well thought out and made our trip much more enjoyable. For us, the convenience outweighed the additional cost. Were there issues? Of course...
1. The truck we had was old - ~196,000 miles. It shimmied and shaked over 45 miles an hour. But how many places on the island can you go that fast anyway. Minor issue.
2. The suicide doors were probably the main issue we had. As the primary driver, it was a pain dealing with opening and closing the doors. Back seat passengers had it far worse having to wait for the front seat people to open.
3. Yes, it is a bit bigger than most other rental pick-ups. Not that much bigger and rarely caused a problem. Think we had to circle twice for downtown parking one time. I am used to parking way out in regular parking lots anyway, so this rarely caused an issue. Minor inconvenience.
4. While the water tank/hose was a major benefit, refilling it was a pain. The dive center we used would not allow us to refill with their hose (water is expensive, I guess). The condo we stayed at did not have an outside hose available either. We bucket brigaded from the condo... Only refilled 3 times, so while a pain, it was another minor inconvenience. No issue at all if you have access to an outside hose...
It was worth it to us, but understand others that think it is too expensive. I'd do it again as it would be hard to go backwards...