If you are concerned about being stuck while you wait for a new heater, then I would do this instead:
Stick with my suggestion of (2) 100w heaters, but get those in addition to the heater you are getting with the kit. Keep that heater (which will be a very basic, inexpensive model) on hand as a spare. You get the peace of mind (from a thermal runaway perspective) of two half sized heaters, but you have the extra one on hand to put into service if need be. The spare heater also has other uses.
You'll find that an extra heater comes in more handy that you realize. I have many tanks, and keep at least 4 or 5 various sized heaters around. I use them for heating quarantine tanks, preheating new water before introducing it, etc.
If you are purchasing new heaters for your tank, I'd recommend the Jager 100W heaters. They will set you back about $20 each. Buy online. In this hobby, you'll observe a dramatic difference between local and online prices. Some great suppliers are Saltwaterfish.com, Marine Depot, Salty Critter, Drs. Foster and Smith, etc. Can't link to them here, but you should be able to find them around.