I'm missing some things here (principal, job owner, ...). I doubt this (and the link to the summary on codeproject) is the recommended way if you want it to be "totally" secure (if that's ever possible).
The articles grant sysadmin and all MSDB roles. What for? This is way too much (in most cases). Plus, you are assigning all 3 msdb roles. You don't want this login to see ALL jobs, right? They should only see their own jobs. Check BOL and see that these roles follow a hierarchy (the most privileged one includes the permission from the other two). It's like people assigning a login the sysadmin server role AND the securityadmin role. The first one already includes all privileges...
You should be assigning a principal (needs only the public server role) access to the proxy, run the job step under the proxy, set the job owner to the SQL login, grant only the SQLAgentUserRole msdb role to the SQL login, set appropriate permissions on the dtsx file and folder it resides in, ...
We did it like this and it works fine. It needs a lot of work and maintenance though.