only the indices are online not the actual deeds - there are abt 25000 deeds officially dating between 1704(Act of Settlement) to late 1847 when the indexing system changed. There are also abt 25000 mortages again nominally from the same dates tho in both cases some deeds date back to early 17th C (1620s or earlier I have found some even earlier) - the index to morts is a right mess in the indices -there are also over 10000 Castletown deeds 1790-1847 (named after the court not the place referred to) + another 1000 or so enrolled deeds - a full index to all these is on my MNB cd rom + summaries of about 10,000.
If you look at MNB www.isle-of-man.com/manxnotebook/towns/peel/prop/property.htm you will get some idea of the utility and nature of this source

The really early deeds are generally in Lib Canc - the index to early deeds included in the index to NSS + SSS deeds is a partial handlist produced by John Quayle CR in early 18th C - again a good number of these on my CD