Configure static

mysite._config.config.yml

---
Name: mysite
After: 'framework/*','cms/*'
---
DateField:
  default_config:
    showcalendar: true
SSViewer:
  theme: 'dna'
i18n:
  locale: 'en_GB'
  date_format: 'dd-MM-yyyy'
MySQLDatabase:
  connection_charset: 'utf8'
---
Only:
  environment: 'dev'
---
BoronService:
  use_dev: 1

mysite.code.services.BoronService.php

<?php
class BoronService extends RestfulService {

    private static $use_dev = 0;
    // ...
}

Debug::show() shows that use_dev is set to 0 and that Debug::show(Director::get_environment_type()); is dev

Solution, thanks to simon_w: $config_use_dev = self::config()->use_dev;