I would recommend going to LRTT if you can, I did a partial mod 13 last year and I would say it was the toughest thing I have done since my initial licence in 1978!!!!!!!
However if you put in the work you should pass.
Doing it through LRTT narrrows the reading scope and is far easier than self study. Fail rate for full and partial mod 13's is low with them. In my view the standard taught is high but the issue is the narrow scope, however it meets the EASA syllabus so they are playing within the rules. The problem lies with EASA.
Be aware the Mod 13 is changing this year so do a little research in to what is happening and the time scales involved. It is getting bigger which is probably to deal with the issue I raise above.