As the owner of YellowLetters.com and calltext.com I can say both direct mail and digital is required to successful. 

Background is originally in SaaS & Digital marketing so I love seeing modern marketing coming to the industry.

Just move from digital conversations to (at least) phone calls. 

Investing in long-term rental properties with the goal of earning a double-digit return can be done—but it requires patience and diligence.

Also do you think its better to avoid mailers and stick with Digital marketing via SEO and PPC only?

Shortcodes are 5-6 digit numbers, example, 818181 the easier to remember the better.

The 10-digit number would be "800-SEL-L4CA" where the "SH" at the end could be omitted; I say could because that main number might rely on those other digits to serve like an extension of sorts.

BTW in 1999 I had a digital camera a lot like this one and I would drive neighborhoods and take pictures then mail the owner an 8.5x5.5 postcard with the pic on it.  

The costs involved in mailers is enormous for the very low response rate.In addition, Many people don't really use the post office that often in a digital cell phone age.

Using 7+ year ownership cuts my results down to single digits for the whole state.. somethings off.