Using a limited math context has significant performance impact, event for the most simple expressions.
Unlimited math context is broken in big-math 2.0.0, and 2.1.0 throws an exception in functions which do not support unlimited context.
For functions which do not support it, limit calculations to 128(or something) so that the rest can continue with unlimited benefits.

MathContext is needed for a lot of the BigDecimal operations. Setting this is currently not supported. At some places MathContext.DECIMAL64 is used, other places a MathContext is created on the fly trying to capture the right precision.
But this must be changed to allow setting of the right MathContext.

Test code

import com.mpobjects.bdparsii.eval.Parser
import org.junit.Test

class MathTest {
    @Test
    fun testMathExpression() {
        println(Parser.parse("239081204214*1247981247912749").evaluate().toPlainString())
        println(Parser.parse("(70*6)/5").evaluate().toPlainString())
    }
}

Except

298368859587470504923124286
84

Result

298368859587470500000000000
420