With my XL sized 7mm semi-dry adequate ditchable weight is not a problem. With a stainless steel backplate I still need 12 lbs of lead to stay neutral at 15 ft with near empty tanks. A 3mm suit on the other hand would probably leave me pretty close to neutral under the same conditions with no weight.
A single steel 72 is hard to beat if you need a tank of more or less standard capacity and have to pack it in to the dive site. The tank is lighter than an AL 80 plus you save 4 or so pounds of lead that does not have to be hauled in as well.
I liked the twin 50's in terms of trim and bouyancy but felt they were a lot of weight for 90 cu ft of air and also not quite enough air if you did a dive that really needed doubles.
I also had problems getting correct fills. 2250 psi fills were common and only slightly higher than the 10% overfill for a + rated 2015 psi tank (which I actually liked). However I had shops blow the burst disc on 2 occasions while filling them to 3000 psi when the guy doing the air fills assumed they had the same service pressure as an AL 50. The first time this happened they replaced the burst disc with one designed for a 3000 psi tank, and then filled them to 3000 psi. This is 134 cu ft of air in a 50 lb package, but then 3000 psi is also only 358 psi less than the hydro test pressure. Scary. The second time it happened they figured it out.
It is not as bad now when tanks come in more than 2 or 3 flavors and people actually look on the shoulder for a service pressure. however it is still a good idea to fill the service pressure markings with some red paint so they stand out, particularly with 1800 psi tanks as they are rare and a little odd.
Steel 50's are in great demand by parents with small divers as they are light, short and hold the right amount of air for a12 yr old diver to keep up with an adult in an AL 80.
