The downside of a month to month lease is that your tenants could leave, but the silver lining is that you can raise the rent when leasing to your next tenant. You could also allow the current tenants to go month to month for an extra 20 or 50/mo.
Keep in mind that your tenants are your customers, so try to keep them happy. If they feel like/think/are of the opinion (perception is reality) they are tied up against their will, they won't like it and may try to retaliate, e.g. damaging the property, making constant maintenance requests, making excuses for paying just past the due date, and otherwise trying to see what they can get away with.
If you only get 12 - 15 months out of a great tenant, that's like hitting a single. Be satisfied with that and get ready for the next pitch.
Summer is a good time to advertise a vacancy, particularly early in the summer when people are moving around prior to the start of the school year. If you find yourself leasing in a slower period you can advertise some kind of move-in special, but keep in mind the DFW market is pretty strong depending on where your property is and the condition of it.
I've been a landlord in FW for ~9 years, so if you would like to discuss further feel free to give me a call/text/email.
comanche3000@live.com
979-450-1994 (cell)