Basically the SH11 is more of a niche PI machine,it only has 2 coil option ie 8'' and the 14x10 Mono,i have used a SH11 but never owned one but i do own both the Garrett coils that have been modified so they fit and work on my Crossbow Pulse,the 14x10 coil is very deep on the CB but that is mainly due too the design of the CB.
The TDI range is in a total different league,i own and use the very last TDI Pro that was sold in the UK,the 'sl' version is slightly less on performance compared with the Pro version,but either the TDI version are far superior as you have a much wider coil selection but the SH11 only has 2 coils available.With the Whites you not only have the 2 factory coils but also a massive wide spectrum of coils from 3rd party supplier like Miner John and even Coiltek,but the massive trump card for the TDI range is the fact that any Minelab GPX/GP Mono coils will work on the TDI range straight out of the box,this gives you a massive array of coils that you can use,i use a wide range of Mono coils from 6'' right upto the massive 20'' Mono coil.......so basically just for that basic advantage the Whites TDI Pro or sl are in a total different league.
The depth from my 20'' mono coil on my TDI is some what amazing especially of course on very large object,also the added bonus with the Whites offering is the ability for using the high/low target conductivity facilty which i must admit does work rather well,depth wise is of course subjective but as yet never really found the maximum depth on large targets with the 20'' Sierra Grande coil,another member on here uses a 24'' Nugget Finder coil on his TDI and that would give you not only extra ground coverage but possibly even more depth on large items,but of course at the expense of smaller single coin size items.
Cannot give a true comment about the SH11 as i dont own one,coils yes i do own and the 14x10 is deep but its a no brainer that the TDI offering with the right coil/s will be deeper as you have a much wider coil selection,at the moment i think i have about 10 coils ranging from 6'' upto 20'' just in the TDI coil arsenal.With the TDI and my couple of Nexus machines and the Fisher TW-5 twin box these machines do offer you a substantial depth gain for large items like cache/hoards.Of course this is just my personal opinion and how i use and hunt with them.
