This is what Steve H. said:
"That is a highly debated and unresolved comparison that has been going on for a number of years. Lots of You Tube videos about White's TDIs.
Technically, they are the same basic schematic diagram. The TDI Pro is simply made from the older larger size components, and the TDI SL made from the more modern smaller surface mount components.
The TDI Pro's Lithium Ion Battery is a big deal if you do much traveling, lots of laws about their handling, shipping, storage, discard, and ownership. Basically it is considered a hazardous chemical. Also it is a heavy model weighing in the 5 lbs range.
The TDI SL was designed to replace the TDI Pro, reducing weight (3 lbs) , and more user friendly batteries. However, 4 hours use per charge with the NiMH. And demand for the TDI Pro continued, thus White's has continued to build it.
Overall user comments tend to indicate the TDI SL is more stable, allows higher gain settings thus more depth. However, the TDI Pro has a strong following with many indicating some performance advantages over the TDI SL.
The comparisons are so close White's has choose to let the buying public decide by continuing to build and sell both, to the point demand decides which of the two is better. However, to date, the buying public has not decided.
As governments make dealing with the Lithium Ion Batteries more and more difficult, and as the older style larger components are becoming obsolete (no longer available), at some point the TDI Pro is not going to be practical to build and sell long before there are any issues with the TDI SL. However, we have not reached that point in time.
Some users prefer and even request the TANK like TDI Pro. If you can take the size/weight, or use the hip option, it is a very old school type design some prefer. However, if smaller/lighter is your thing, the TDI SL is a better choice.
For most new user, the "splitting hairs" performance differences or comparisons are negligible. The 3 lbs and non-hazard batteries of the TDI SL typical win out over TANK like design.
Howard "
Jim
