Their web site
According to our best orbit fit and using regular assumptions on phase angle
correction, the H value es around 0.3. Unfortunately we do not know the
geometric albedo but if below 0.25 (which is the case of all TNOs for which an
albedo has been measured except Pluto), the object would be larger than Pluto.
However, it may well happen that this object is abnormally bright (with a very
high albedo), like Pluto. So, depending on the albedo, this object might be sort
of a Pluto's brother or Pluto's father...
This object is beyond Pluto and almost reachable by most amateurs, which is the
reason why we write here!. It is observable right after sunset for a while at a
reasonable elevation. Maybe some decent science can still come out of your
Time will tell if it is a legitimate huge find. The size/population numbers have always indicated that there should probably be at least one more Pluto-size object out there, and I always believed someone would find it. Early KBO papers after the discovery by Jewitt and Luu of 1992 QB1 discussed the size distribution with Pluto at the top and kept the option open of other big ones.