Howdy O! Sensei
In Texas, Commercial Real Estate and Residential Real Estate are regulated differently. Commercial is more like any other business deal. Residential is regulated because they sought to protect naive Buyers & Sellers of residential property by requiring Texas Real Estate Commission (TREC) published forms for the transaction to be legal to start with.
As I said earlier, any means of making an agreement between the parties is likely OK when agreed upon 'twixt the parties. The issue really only arises when there is some dispute later on.
The stamps on stuff are still in wide use. There is however "chain of custody" of the stamps themselves.
The services I examined a while back had no facility for uploading one's own signature if it existed locally... they made you pick from a small variety of Script Fonts and you agreed that that was now your signature for that session - recording your consent in the file's archive.
What surprises me most about this agreement is that the other party did not initiate the process using a service to begin with. It is really cheap (MUCH less than courier/FedEx, etc.) - in a Residential RE deal, the offers and counters where a BIG cost at closing for document logistics. Our Digital sigs we implemented with the "Clipboard Tablet Capture" actually embedded the sigs/initials into the file - then just send it via our auto-email or attach to en email of your own. ANY change - one character anywhere and the file/software zapped all the sigs. The "Best Evidence" still remained the actual "Last Signed" accepted agreement. Oh! Did I mention that the parties were actually signing with real ink pen (it had the added feature of being the "Wacom" pen too)
company is http://autorealty.com if you wanna check it out. If I know the owner like I think I do, they are WAY late to the party with iDevice Apps.