Daniel,
I know this topic has been covered here in detail before, so you might want to do some searching too.
I also use a SDIRA, but have not borrowed yet as the properties I am targeting are not 'eligible' in most Non-recourse lenders opinion, since they are houses converted to duplexes, pre 1940 construction, and under 100K purchase price. This is also my first year, so have yet to do the actual book keeping of what I am going to say below, so take it with a grain of salt! It is what I understand things to be from what I have learned here on BP.
As far as the whether to leverage or not..... to me it is a no brainier if you can. With that said, I look mainly at 'return on my investment'. Save you have 100K to invest and you can buy one property for 100K, or leverage it into 3 100K properties.
For rough numbers, let's say you make an 8% return with out appreciation, or 11% with appreciation, on the all cash unit. This might give you a NOI of about 8K, which is also your cash flow since there is no interest or principal payments. Hence your 8% return on the 100K.
If you leverage your money and get those 3 100K properties, looking at your return on your investment/equity, you might be at about 14% without appreciation or 24% with appreciation. This might give you a NOI of about 25K, but you then deduct interest of say 11K for a cash flow of 14K (hence your 14% return) and you also get depreciation of about 11K, leaving you a taxable income of 3K. It the UDFI is 33% in rough numbers, you only owe a tax of 1K.
This means by leveraging within your SDIRA, even AFTER you pay the UDIF, you have raised your return from 8% to 13% or almost 60% better. If you factor in appreciation, the return might go from 11% to 22%, or 100% better (doubling your return).
Again, these are just my THOUGHTS. Maybe @Steven Hamilton II could chime in and give his input on this line of thinking too.
Dan Dietz