I can't figure out why the TM751 would be safer than the TW523 but experiences vary.
I've been completely satisfied with my 'home automation' for several years now. Consequently I don't get out much anymore regarding X10.
However I was surprised to see that the PSC05/TW523 have all but disappeared in my absence. Those left seem to sell at scalping prices.
Enddoc, please feel free to use whatever you wish from my blog under the condition that you don't call me Mr. 
BTW, I have been working with someone who is adding my PSC05/TW523 'receive' code into Tom Igoe's x10.lib. Finally, send and receive will both be in one lib.
John