Just doing my job to deliver this PSA... I have used frontier and without getting too long-winded STAY AWAY FROM FRONTIER. At best it's a completely disorganized, poorly functioning "volunteer service". At worst they are led by false advertising to steal your money. I sincerely believe it is the latter. I spent roughly 25 weeks in one form or another with Frontier. The London staff is laughable. They don't pay their field staff (some of which are terrible and others are good) or support the projects above the bare minimum. The living conditions are awful compared to how much you're paying and you can see the minimal investments into improving this.
The lodging/equipment was falling apart and constantly breaking. Also, don't expect the money to be used for the cause you actually signed up or care about. It's painfully obvious after my time with them that all the money goes to (misleading) advertising and lawyers (and I'm sure to the board members of this so-called "nonprofit" which is likely a front for tax purposes). They only survive by new volunteers getting tricked by their slick ads and website but be warned they will try to steal your money. I was swindled out of over 2000 USD. And they know the cost of trying to sue them is prohibitively expensive to try to do, and they purposely make you sign ambiguous contracts to make sure they don't have to refund you even if they cancel the project/trip on you. Bottom line. Avoid at all costs.
My recommendation, if you know where or what kind of project you'd like to do, search for local NGOs, etc. You'll save a ton of money, use your money to actually support your desired cause and it'll probably be much more functioning and pleasant. Also in regards to the terrible field staff, they hire anyone with or without any knowledge or credentials often. Had one "guide" that was harassing one of the other volunteers. Another that made up rules, at one point walked away while crying was just an absolute mess from day 1.