They contacted me via email 2 or 3 years ago and I was dubious as well. Did quote and get the work but it wasn't worth it for me, think it was about 5 or 6 hours per week. Just doing communal areas in a couple of blocks of new flats. Stuck it out for about 6 months, it was just too far away from me to manage such a small site and it was always difficult getting staff in that particular area, if they would have had more work in the area it would have been a very good contract!
If the work is local to you it might be worth your while especially if there is the possibility of more work in the future. They will probably want the windows cleaning as well, which we used to sub out.
Pretty good payers and the first company to ever contact me via email, go for it and good luck.